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    ANNUAL REPORT Center for Experimental Nuclear Physics and Astrophysics University of Washington April, 2011 Sponsored in part by the United States Department of Energy under Grant #DE-FG02-97ER41020.


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    This report was prepared as an account of work sponsored in part by the United States Government. Neither the United States nor the United States Department of Energy, nor any of their employees, makes any warranty, expressed or implied or assumes any legal liability or responsibility for accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe on privately-owned rights. Cover design by Nora Boyd. Top photos, left to right: Graduate student Ran Hong examining the 6 He collection system in experimental cave 1 (see Sec. 3.3.1). Photo by Greg Harper. Gravity graduate student Charlie Hagedorn, self portrait, with the submillimeter parallel- plate torsion balance (see Sec. 2.1.3). Photo by Charlie Hagedorn. Postdoc Andrew Wagner, research engineer Nora Boyd, graduate student Michael Hotz, postdoc Gray Rybka, and senior research engineer Doug Will removing the bottom of the ADMX insert (see Sec. 5.1). The ADMX magnet cryostat is in the background. Photo by Greg Harper. Bottom photo: Instrument maker Jim Elms discussing the new NCD end cap assemblies for the HALO experiment (see Sec. 1.6) with Hamish Robertson. The end caps are being manufactured in production mode with our new CNC lathe. Photo by Greg Harper.


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    UW CENPA Annual Report 2010-2011 April 2011 i INTRODUCTION The Center for Experimental Nuclear Physics and Astrophysics, CENPA, was established in 1998 at the University of Washington as the institutional home for a broad program of research in nuclear physics, astrophysics and related fields. Research activities are conducted locally and at remote sites. CENPA has been a major participant in the Sudbury Neutrino Observatory (SNO) and is presently contributing substantially to the KATRIN tritium beta decay experiment, the MAJORANA 76 Ge double beta decay experiment, and the SNO+ 150 Nd double beta decay experiment in Canada. With the arrival of the Muon Physics group from Illinois we have new activities at the Paul Scherrer Institute in Switzerland, and development of a new program to measure the anomalous magnetic moment of the muon at Fermilab. The fundamental symmetries program also includes “in-house” research using the local tandem Van de Graaff accelerator, and neutron physics at other locations. We conduct user-mode research on relativistic heavy ions at the Relativistic Heavy Ion Collider at Brookhaven. The year 2010–2011 has been filled with new activity at CENPA. Professors David Hertzog and Peter Kammel arrived from the University of Illinois, bringing with them Postdoctoral Fellow Peter Winter and students Michael Murray and Sarah Knaack. They will continue to receive support for some of their research for the duration of their 3-year NSF grant until April 2012, thanks to the cooperation of the University of Illinois and the NSF. Worldwide interest in their previous result for muon g − 2, which shows approximately 3σ disagreement with the Standard Model calculation, continues unabated, and their new proposal to mount a still more precise measurement at Fermilab has been greeted with enthusiasm. The KATRIN experiment, sited in Karlsruhe, continues to move forward with construc- tion. The difficult task of building the windowless gaseous tritium source passed a major milestone with the delivery and testing of the “demonstrator”, a cryogenic-performance pro- totype. Remarkably, temperature stability of 4 mK at 30 K was achieved, almost 10 times better than the specification. Here at CENPA, good progress on the detector system has brought us close to a successful conclusion to commissioning, and the complete system will be shipped in the spring of 2011. Professor Leslie Rosenberg’s group succeeded, with the skillful support of Doug Will, in bringing the 12-tonne superconducting magnet for the axion experiment ADMX from Livermore to Seattle. There was no damage or misadventure, as determined by a complete cooldown and ramping of the magnet field to 6 T. We await completion of the modification to our high-bay area east of the tandem which will allow sufficient headroom to install and remove the insert. We are very interested in the potential of “Project 8,” a possible approach to extending the sensitivity of direct neutrino mass measurements below even the 200-meV level accessible to KATRIN. A prototype microwave receiver and antenna are being installed in the bore of a superconducting magnet that was formerly used by Professor Bob Van Dyck. We take this opportunity to congratulate CENPA Fellow Mike Miller and Postdoctoral Fellow Gray Rybka, who teamed up to write a successful proposal to the Royalty Research Foundation for Project 8. With Associate Director Greg Harper assuming his new duties, we carried out a search for


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    ii a professional staff member to maintain our strength in technical support, especially in the face of so much new activity. We are very pleased to welcome Nora Boyd to our professional staff. Two senior Postdoctoral Fellows, Seth Hoedl and Brent VanDevender, took up positions elsewhere, Seth moving to a startup company in North Carolina, and Brent taking a staff position at Pacific Northwest National Lab. We were successful in recruiting Diana Parno from Carnegie-Mellon University into a postdoc position, and she joined us in April, 2011. Frederik Wauters from Leuven, Belgium, will join us in June, 2011. The DOE Office of Nuclear Physics, which provides operating support through programs in Low Energy Nuclear Physics and Heavy Ion Physics, has renewed our support under Grant DE-FG02-97ER41020 for FY11, which began December 1, 2010, and is the third of the current 3-year cycle. In the following paragraphs we record some more of the highlights of our past year in research. • Analysis of the data from emiT-II has been completed. We have not found evidence for Time-Reversal symmetry breaking, but we have placed the best limit on the D coefficient significantly below any previous experiment. This important achievement had a strong contribution from UW. The apparatus upgrade from emiT-I was per- formed mostly at UW. Over the last few years, at UW, we remained responsible for the Monte Carlo calculations, which played an important role in understanding systematic uncertainties in the experiment. We are presently writing a paper for publication. • We have determined the 22 Na(p, γ) thermonuclear reaction rate for novae and have found large discrepancies with a previous experiment. Our results imply that the chance of observing the highly-sought (but so-far elusive) evidence of production of 22 Na in novae is a bit harder than previously thought. • We have performed and published the results of several experiments related to under- standing details of nova nucleosynthesis. • We have succeeded in our efforts on production of 6 He with the aim of searching for tensor contributions to the weak current. We demonstrated that we can consistently get ∼ 109 atoms/s of 6 He delivered to a clean room. We are now on the process of moving the laser systems from Argonne National Lab to UW. • The UCNA collaboration has published a determination of the beta asymmetry to approximately 1%. We have played a supporting role in experimental shifts, data analysis, and in writing the publications. • The earthquake and tsunami that struck Japan March 11, 2011, caused severe damage to the reactor complex at Fukushima. We set up a monitoring system that took ad- vantage of the very high airflow rates through intake filters at the Physics-Astronomy Building, as well as a test PPC detector for MAJORANA that was available. We were able to see the arrival of fission products, quantify their activity in the air, and draw conclusions about some of the circumstances of events at Fukushima.


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    UW CENPA Annual Report 2010-2011 April 2011 iii • The UW URHI group has established accurate systematic trends for minimum-bias jet (minijet) production in Au-Au and Cu-Cu collisions by application of pileup correction techniques developed by our group (collision-event pileup is increasingly significant for higher-luminosity RHIC operation). After pileup corrections the previously-observed “sharp transition” in minijet properties now clearly occurs at a specific mean projectile- nucleon path length for all collision systems corresponding to at least two dijets per collision. We have converted jet angular correlations into jet fragment yields via pQCD dijet cross sections. The fragment yields account for essentially all hadron yield in- creases beyond participant (wounded-nucleon) scaling in Au-Au collisions, indicating that jet absorption in an opaque medium is negligible, although jets are strongly mod- ified. • We have established an accurate global parametrization of our azimuth quadrupole measure v2 {2D} which is factorized on centrality b, transverse momentum pt and col- √ lision energy sN N . Our v2 {2D} data, obtained by fits to 2D angular correlations, are precisely distinguished from jet correlations (“nonflow”). Our v2 parametrization challenges conventional interpretations of published v2 data in terms of hydrodynamic flows and constituent-quark recombination, suggesting instead a possible QCD field- √ field interaction mechanism for A-A collisions above sN N ≈ 13 GeV. • We have used our jet and quadrupole systematics to relate RHIC collisions to recent results from the LHC at 7 TeV, specifically the “ridge” observed by the CMS collabo- ration. We have demonstrated that jet correlations in 7 TeV p-p collisions are exactly as predicted by a simple extrapolation from 200 GeV data (multiplicative factor 2.3), and that the CMS ridge is the result of a subtle interplay between jet and quadrupole correlation components as affected by applied multiplicity and pt cuts. Three CENPA graduate students, Rob Johnson, Mike Marino, and Anne Sallaska, ob- tained their Ph.D. degrees during the period of this report. Rob is a postdoc at the University of Colorado in Boulder, Mike is a postdoc at the Technical University, Munich, and Anne is a postdoc at the University of North Carolina, Chapel Hill. As always, we encourage outside applications for the use of our facilities. As a con- venient reference for potential users, the table on the following page lists the capabilities of our accelerators. For further information, please contact Greg Harper, Associate Direc- tor, CENPA, Box 354290, University of Washington, Seattle, WA 98195; (206) 543 4080, or gharper@u.washington.edu. Further information is also available on our web page: http://www.npl.washington.edu. We close this introduction with a reminder that the articles in this report describe work in progress and are not to be regarded as publications or to be quoted without permission of the authors. In each article the names of the investigators are listed alphabetically, with the primary author underlined, to whom inquiries should be addressed. Hamish Robertson, Director Victoria Clarkson, Assistant Editor Greg Harper, Associate Director and Editor Gary Holman, Technical Editor


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    iv TANDEM VAN DE GRAAFF ACCELERATOR A High Voltage Engineering Corporation Model FN purchased in 1966 with NSF funds, operation funded primarily by the U.S. Department of Energy. See W. G. Weitkamp and F. H. Schmidt, “The University of Washington Three Stage Van de Graaff Accelerator,” Nucl. Instrum. Methods 122, 65 (1974). Recently adapted to an (optional) terminal ion source and a non-inclined tube #3, which enables the accelerator to produce high intensity beams of hydrogen and helium isotopes at energies from 100 keV to 7.5 MeV. Some Available Energy Analyzed Beams Ion Max. Current Max. Energy Ion Source (particle µA) (MeV) 1H or 2 H 50 18 DEIS or 860 3 He or 4 He 2 27 Double Charge-Exchange Source 3 He or 4 He 30 7.5 Tandem Terminal Source 6 Li or 7 Li 1 36 860 11 B 5 54 860 12 C or 13 C 10 63 860 ∗14 N 1 63 DEIS or 860 16 O or 18 O 10 72 DEIS or 860 F 10 72 DEIS or 860 ∗ Ca 0.5 99 860 Ni 0.2 99 860 I 0.001 108 860 *Negative ion is the hydride, dihydride, or trihydride. Several additional ion species are available including the following: Mg, Al, Si, P, S, Cl, Fe, Cu, Ge, Se, Br and Ag. Less common isotopes are generated from enriched material. We recently have been producing the positive ion beams of the noble gases He, Ne, Ar, and Kr at ion source energies from 10 keV to 100 keV for implantation, in particular the rare isotopes 21 Ne and 36 Ar. We have also produced a separated beam of 15-MeV 8 B at 6 particles/second.


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    Contents INTRODUCTION i 1 Neutrino Research 1 1.1 Neutrino research at CENPA . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 KATRIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 Overview of the KATRIN experiment . . . . . . . . . . . . . . . . . . . . . . 2 1.2.1 Status of the U. S. contribution to the KATRIN experiment . . . . . 4 1.2.2 Commissioning the KATRIN detector . . . . . . . . . . . . . . . . . . 6 1.2.2.1 Commissioning the detector and electronics . . . . . . . . . 7 1.2.2.2 Status of the magnets . . . . . . . . . . . . . . . . . . . . . . 8 1.2.2.3 Status of the vacuum system . . . . . . . . . . . . . . . . . . 8 1.2.2.4 Status of the calibration system . . . . . . . . . . . . . . . . 9 1.2.2.5 Status of the veto . . . . . . . . . . . . . . . . . . . . . . . . 10 1.2.2.6 Status of the DAQ and slow controls . . . . . . . . . . . . . . 10 1.2.2.7 Near-time analysis tools . . . . . . . . . . . . . . . . . . . . 11 MAJORANA . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.3 MAJORANA DEMONSTRATOR Activities . . . . . . . . . . . . . . . . . . . . . 13 1.3.1 A Monte-Carlo model of the background energy spectrum of the MALBEK detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.3.2 Pre-amplifier with forward biased reset for MAJORANA . . . . . . . . 16 1.3.3 Digitizer evaluation with PPCII . . . . . . . . . . . . . . . . . . . . . 17 1.3.4 Design, fabrication and testing of HV and signal cables and connectors for the MAJORANA experiment . . . . . . . . . . . . . . . . . . . . . . 18 1.3.5 Searches for dark matter with a MAJORANA prototype . . . . . . . . 19 1.3.6 Data management and workflow management for the MAJORANA DEMONSTRATOR . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20


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    vi SNO+ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 1.4 Overview of the SNO+ experiment and CENPA’s contribution . . . . . . . . 21 1.4.1 Status of the SNO+ data acquisition software . . . . . . . . . . . . . 22 1.4.2 Status of the SNO+ slow control hardware readout . . . . . . . . . . 23 1.4.3 Status of the SNO+ slow control software . . . . . . . . . . . . . . . . 24 1.4.4 The electron energy scale linearity of SNO+ scintillator . . . . . . . . 24 1.4.5 Measurement of the refractive index of SNO+ scintillator . . . . . . . 25 Project 8 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26 1.5 Status of the Project 8 neutrino mass measurement prototype . . . . . . . . 26 HALO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29 1.6 The HALO supernova detector . . . . . . . . . . . . . . . . . . . . . . . . . . 29 SNO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 1.7 Overview of the SNO experiment and CENPA’s contribution . . . . . . . . . 30 2 Fundamental symmetries and non-accelerator based weak interactions 32 Torsion balance experiments . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 2.1 Overview of the CENPA torsion balance experiments . . . . . . . . . . . . . . 32 2.1.1 Testing an equivalence principle pendulum with hydrogen-rich test bodies 32 2.1.2 Progress toward improved equivalence principle limits for gravitational self-energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 2.1.3 Submillimeter parallel plate test of gravity update . . . . . . . . . . . 34 2.1.4 Progress on the wedge-pendulum probe of short-range gravity . . . . 35 2.1.5 Experimental limits on a proposed signature of space-time granularity from a spin polarized torsion pendulum . . . . . . . . . . . . . . . . . 36 2.1.6 Status update on a new torsion balance test of spin coupled forces . . 37 2.1.7 Progress towards an equivalence principle test using a cryogenic torsion balance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37 2.1.8 Development of an ultrasensitive interferometric quasi-autocollimator 38


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    UW CENPA Annual Report 2010-2011 April 2011 vii Non-accelerator based weak interactions and fundamental symmetries . 39 2.2 Overview of non-accelerator based weak interactions studies . . . . . . . . . . 39 2.2.1 Status of the UCNA experiment . . . . . . . . . . . . . . . . . . . . . 39 2.2.2 Permanent electric dipole moment of atomic mercury . . . . . . . . . 40 2.2.3 Parity non-conserving neutron spin rotation experiment . . . . . . . . 41 2.2.4 Progress in analysis of emiT data . . . . . . . . . . . . . . . . . . . . 41 3 Accelerator based physics 43 Nuclear astrophysics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 3.1 Overview of the CENPA nuclear astrophysics program . . . . . . . . . . . . . 43 3.1.1 Direct measurements 22 Na(p,γ)23 Mg resonances . . . . . . . . . . . . 43 3.1.2 Thermonuclear 25 Al(p,γ)26 Si reaction rate from 26 P beta decay . . . 44 3.1.3 Measurements of 33 S(p,γ)34 Cl at nova temperatures: results . . . . . 45 3.1.4 Miscellaneous studies of nova nucleosynthesis . . . . . . . . . . . . . . 46 Nuclear structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 3.2 Overview of the CENPA nuclear structure program . . . . . . . . . . . . . . . 47 3.2.1 Electron capture on 116 In and 2β decay . . . . . . . . . . . . . . . . . 47 3.2.2 Properties of 20 Na, 24 Al, 28 P, 32 Cl, and 36 K . . . . . . . . . . . . . . 48 3.2.3 Development of thin ion-implanted targets for precision studies . . . 49 3.2.4 Calculations of isospin symmetry breaking in nuclei . . . . . . . . . . 50 Accelerator based weak interactions . . . . . . . . . . . . . . . . . . . . . . . 50 3.3 Overview of the CENPA accelerator based weak interactions program . . . . 50 3.3.1 Production of 6 He at CENPA . . . . . . . . . . . . . . . . . . . . . . 51 3.3.2 Neutron shield for 6 He β decay experiment . . . . . . . . . . . . . . . 52 3.3.3 Helium recirculation developments for 6 He laser trap . . . . . . . . . . 53 3.3.4 Precision determination of the 6 He half-life . . . . . . . . . . . . . . . 53 3.3.5 Development of a 114m In source of conversion electrons . . . . . . . . 54


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    viii 3.3.6 M1 width of the 2+ 1 state in 22 Na and searches for tensor contributions to beta decays. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55 4 Precision muon physics 57 4.1 Overview of the muon physics program . . . . . . . . . . . . . . . . . . . . . 57 MuCap . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59 4.2 Overview of MuCap experiment physics and technique . . . . . . . . . . . . 59 4.2.1 Singlet capture rate analysis . . . . . . . . . . . . . . . . . . . . . . . 61 4.2.2 Molecular transfer analysis . . . . . . . . . . . . . . . . . . . . . . . . 62 MuSun . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 4.3 Muon capture on deuterium, the MuSun experiment . . . . . . . . . . . . . . 63 4.3.1 TPC performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65 g-2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 66 4.4 Overview of the g-2 experiment: physics, technique and project status . . . . 66 4.4.1 Current Status of Cross Section Measurements via ISR at Belle . . . . 68 5 Axion searches 70 ADMX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 5.1 ADMX axion search . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 70 Axion torsion balance experiment . . . . . . . . . . . . . . . . . . . . . . . . . 74 5.2 Improved constraints on an axion-mediated force . . . . . . . . . . . . . . . . 74 5.3 A magnet upgrade for the “axion” torsion-balance experiment . . . . . . . . 75 6 Relativistic Heavy Ions 76 6.1 UW URHI program overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 6.1.1 Minijets (minimum-bias jets) in correlations and spectra . . . . . . . 77 6.1.2 The azimuth quadrupole in correlations and spectra . . . . . . . . . . 78 6.1.3 Current status and plans . . . . . . . . . . . . . . . . . . . . . . . . . 79 6.2 Global parametrization of the azimuth quadrupole in Au-Au collisions . . . . 80


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    UW CENPA Annual Report 2010-2011 April 2011 ix 6.3 pt and charge dependence of the same-side jet peak in Au-Au collisions . . . 80 6.4 Quadrupole Spectrum . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82 6.5 Single-particle jet fragment yields from two-particle jet correlations - compar- isons with pQCD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 83 6.6 Interpretation of the same-side “ridge” observed in LHC p-p angular correla- tions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84 6.7 First correlation analysis of low-energy RHIC data at 39 and 7.7 GeV . . . . 85 6.8 Consequences of event-pileup corrections to inferred minijet systematics . . . 86 6.9 Testing the HIJING Monte Carlo as a linear-superposition reference for Au-Au collisions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 6.10 Glasma flux tubes and collective expansion vs minimum-bias jets . . . . . . 88 6.11 “Triangular flow” vs minimum-bias jets in long-range (on η) correlations . . 89 7 Radiation and detectors and other research 91 7.1 Interaction of charged particles with matter . . . . . . . . . . . . . . . . . . . 91 7.1.1 Differences in M0 and M1 for B-F and FVP. . . . . . . . . . . . . . . 92 7.1.2 Applications for STAR, ALICE, ILD, etc. . . . . . . . . . . . . . . . 92 7.1.3 Applications in KATRIN . . . . . . . . . . . . . . . . . . . . . . . . . 93 7.1.4 Dosimetry of C-ion beams for radiation therapy . . . . . . . . . . . . . 93 7.1.5 Comparisons with functions calculated with GEANT4 . . . . . . . . . 93 7.2 Status of nonlocal quantum communication test . . . . . . . . . . . . . . . . 94 7.3 Detection of airborne fission products from the Fukushima reactor incident . 96 8 Facilities 98 8.1 Facilities overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98 Computing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 8.1.1 Laboratory computer systems . . . . . . . . . . . . . . . . . . . . . . . 100 CENPA electronics shop . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101 8.1.2 Electronic equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . 101


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    x Accelerator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102 8.1.3 Van de Graaff accelerator and ion source operations and development 102 CENPA instrument shop . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 8.1.4 CENPA instrument shop and student shop . . . . . . . . . . . . . . . 103 Building modifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 8.1.5 Buildings, accommodating the ADMX cryostat . . . . . . . . . . . . . 103 9 CENPA Personnel 105 9.1 Faculty . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105 9.2 CENPA External Advisory Committee . . . . . . . . . . . . . . . . . . . . . . 105 9.3 Postdoctoral Research Associates . . . . . . . . . . . . . . . . . . . . . . . . 106 9.4 Predoctoral Research Associates . . . . . . . . . . . . . . . . . . . . . . . . . 106 9.5 NSF Research Experience for Undergraduates participants . . . . . . . . . . . 106 9.6 University of Washington graduates taking research credit . . . . . . . . . . . 107 9.7 University of Washington undergraduates taking research credit . . . . . . . . 107 9.8 Professional staff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107 9.9 Technical staff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 9.10 Administrative staff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 9.11 Part time staff and student helpers . . . . . . . . . . . . . . . . . . . . . . . 108 10 Publications 109 10.1 Published papers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 10.2 Papers submitted or to be published 2011 . . . . . . . . . . . . . . . . . . . . 114 10.3 Invited talks, abstracts, and other conference presentations . . . . . . . . . . 114 10.4 Patents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117 10.5 Ph.D. degrees granted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 117


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    UW CENPA Annual Report 2010-2011 April 2011 1 1 Neutrino Research 1.1 Neutrino research at CENPA R. G. H. Robertson Neutrino research is a major focus of CENPA’s current research effort, and we are contributing significantly to 6 projects which are in different stages. The Sudbury Neutrino Observatory (SNO) project led to the resolution of the solar neutrino problem in favor of new neutrino properties (mass and oscillations). Data taking ended in 2006, but much interesting physics remained to be mined, and that process is now drawing to a conclusion. Recent publications include a very detailed re-analysis of the data from the first two phases with an improved rejection of low-energy backgrounds. That neutrinos have mass is established from oscillations, but the mass itself is not known. Neutrino mass is not only an important fundamental constant, it influences the evolution of the cosmos. In 2000 we joined the KATRIN collaboration as founding members and took on the task of delivering the detector system for this complex experiment. The goal is a direct determination of neutrino mass from tritium beta decay with a sensitivity of 200 meV. Our construction of the detector system is nearly complete and it will be shipped to Germany in the spring of 2011. The question of why the universe is mostly matter, with very little antimatter, may reflect a unique property of neutrinos. Alone among matter particles, neutrinos can be their own antiparticles, but it is not known if they are. If they are then they can provide a mechanism for the conversion of antimatter to matter. The only known approach to answering this question is to search for neutrinoless double beta decay. The MAJORANA DEMONSTRATOR is a search in 76 Ge using enriched and natural Ge detectors. At CENPA we are contributing mechanical design and fabrication, low-background cables and components, and electronics. The SNO+ experiment is similarly motivated but will carry out the search for neutrinoless double beta decay in 150 Nd, making use of the former SNO detector in a new incarnation. The acrylic vessel will be filled with a Nd-doped liquid scintillator and a search made for a monoenergetic line at the known Q-value. KATRIN is the most sensitive direct mass search experiment, but it may nevertheless turn out that the mass is less than 200 meV. Oscillations place a lower limit of 20 meV on the average mass of the 3 eigenstates. We are beginning experimental investigation of a new idea for a tritium beta decay search that might reach into this last window. “Project 8,” as it is called, would make use of cyclotron radiation emitted by betas spiraling in a magnetic field. The only supernova neutrino burst to be detected came from SN1987a. There is much to be learned about supernovae from neutrinos and an opportunity presented itself with the conclusion of the SNO experiment to make use of the neutral-current-detection (NCD) array that we built. A supernova detector, HALO, based on Pb as a target and using the NCD detectors is under construction in SNOLAB.


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    2 KATRIN 1.2 Overview of the KATRIN experiment J. F. Amsbaugh, J. Barrett∗ , A. Beglarian† , T. Bergmann† , L. I. Bodine, T. H. Burritt, T. J. Corona‡ , P. J. Doe, S. Enomoto, J. A. Formaggio∗ , F. M. Fraenkle‡ , D. L. Furse∗ , G. C. Harper, M. Knauer† , A. Kopmann† , E. L. Martin, N. S. Oblath∗ , L. Petzold† , D. Phillips‡ , A. W. P. Poon§ , R. G. H. Robertson, M. Steidl† , D. Tcherniakhovski† , B. A. VanDevender∗ , T. D. Van Wechel, B. L. Wall, K. J. Wierman, J. F. Wilkerson‡ , and S. Wüstling† The KATRIN experiment aims to make an order of magnitude improvement in the direct measurement of the mass of the neutrino complementing the model-dependent measurements obtained via cosmology and searches for neutrinoless double beta decay. With a predicted sensitivity of 200 meV, KATRIN will investigate the neutrino hierarchy and address the value for the neutrino mass of 560 meV derived from a claimed observation of neutrinoless double beta decay1 . KATRIN is currently under construction at the Karlsruhe Institute of Technology (KIT) in Germany. Data taking is expected to begin in early 2014 with final sensitivity reached 5 years later. KATRIN probes the neutrino mass by making a precision measurement of the electron energy spectrum associated with beta decay of tritium. Neutrino mass is evidenced in a distortion at the high energy tail of the spectrum, allowing a value for the mass to be derived solely from the kinematics of the reaction. The design of the KATRIN apparatus draws on some 40 years of tritium beta decay searches for the neutrino mass. The improved sensitivity of KATRIN arises primarily from increases in source luminosity and the physical size of the apparatus and probably represents the best one can practically expect to achieve with this technology. The layout of the KATRIN apparatus is shown in Fig. 1.2-1. The tritium source is of the window-less, gaseous type, a 10-m long, 9-cm diameter tube containing tritium gas at an effective column density of 5 × 1017 molecules/cm2 and a tem- perature of 30 K. Tritium escaping from the ends of the source is returned to the center by way of turbo molecular pumps, the differential pumping system. Electrons from tritium beta decay are constrained to escape from the ends of the source via a train of 3-T magnets. Those electrons escaping “downstream” pass towards the analyzing spectrometers via the cryogenic pumping system which consists of a chicane beam pipe whose walls are coated with argon frost to trap any escaping tritium molecules that would contaminate the spectrometer system. The tritium pressure at the entrance to the spectrometers is 11 orders of magnitude lower than the pressure at the outlet of the tritium source. ∗ Massachusetts Institute of Technology, Cambridge, MA. † Karlsruhe Institute of Technology, Karlsruhe, Germany. ‡ University of North Carolina, Chapel Hill, NC. § Lawrence Berkeley National Laboratory, Berkeley, CA ∗ Pacific Northwest National Laboratory, Richland, WA. 1 H. V. Klapdor-Kleingrothaus, I. V. Krivosheina, A. Dietz, and O. Chkvorets, Phys. Lett. B 586, 198 (2004).


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    UW CENPA Annual Report 2010-2011 April 2011 3 Tritium source Transport section Pre spectrometer Spectrometer Detector eV !E = 0.92 V E > 18.3 ke e- ve - 3H - - 1 e /s e e e- e- ! decay e- 3 - 10 e /s 1010 e- /s 10 10 e- /s 3He 3H eV 3He E = 18600 ~70 m ! Figure 1.2-1. Layout of the KATRIN experiment showing the principal components. Also shown is the electron flux for each stage of the apparatus KATRIN employs two spectrometers of the adiabatic retarding potential type which make use of a precise electrostatic potential to energy-select electrons for passage through the spectrometer. The purpose of the first spectrometer, the pre-spectrometer, is to reject all but the interesting highest energy electrons, within approximately 300 eV of the tritium endpoint. This reduces the flux of electrons from 1010 e− /sec to 103 e− /sec. The electrons then enter the main spectrometer. In order to reduce electron scattering, the pressure inside the spectrometer is maintained at 10−11 mbar. Both spectrometers have wire-planes that conform to the inner shell of the spectrometer vessel, both shaping the electric field potential and reducing sources of background electrons. By precisely controlling the retarding potential on these wire planes, an energy resolution of 0.93 eV is achieved. A monitoring spectrometer, observing a line from a Kr source and supplied with the same retarding potential as the main spectrometer, is used to record the stability of the retarding potential in the main spectrometer. Only those electrons with sufficient energy to overcome the variable retarding potential pass through the main spectrometer to the electron detector. Thus the spectrometer makes an integral measurement of the electron flux. The rate of tritium beta decay electrons exiting the main spectrometer and seen by the detector is approximately 1 Hz. In principle it is only necessary for the electron detector to count electrons. In practice, energy, spatial, and temporal information is very important in both understanding the operation of the apparatus and sources of systematic background. The detector, shown in Fig. 1.2-2, is a monolithic PIN diode array consisting of 148 pixels arranged in a “dart board” pattern which provides the spatial information. Typical energy resolutions of individual pixels are 1.4 keV (FWHM). Signal to back- ground rates directly effect the run time to reach maximum sensitivity. To suppress intrinsic backgrounds the detector is surrounded by lead and copper shielding. Backgrounds associ- ated with cosmic rays are tagged using a cylindrical plastic scintillator veto surrounding the detector. Signals from the PIN diode array and the veto are read out using custom designed


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    4 ! Figure 1.2-2. The KATRIN detector assembly. Left: the detector wafer showing “dart- board” layout of the pixels. Center: the detector mounting flange showing the pogo pin contacts to the pixels. Right: the preamplifier carousel mounted immediately behind the detector and connected by the pogo pins. analog and digital electronics provided by KIT while data acquisition is controlled by soft- ware provided by the US collaborators. KIT is an ideal location for the KATRIN experiment since it has the necessary license and expertise to handle the large quantities of tritium re- quired for a bright source. Currently the experiment is in an intense construction phase. The buildings housing the apparatus are complete. All three spectrometers are installed. The pre-spectrometer has been extensively used to understand sources of background such as Penning traps and to use this understanding to refine the design of the wire-planes of the main spectrometer. Installation of the wire-planes and other hardware associated with the main spectrometer is expected to be finished in August 2011 after which the US supplied detector system will be used in commissioning the main spectrometer. The detector system is described in detail below and is expected to meet the schedule and performance requirements of the main spectrometer commissioning. The differential pumping system was delivered to KIT in June 2010 and has successfully passed its acceptance test and is now undergoing tests to demonstrate that it can satisfy the physics criteria. The cryogenic pumping system is on track to be delivered to KIT in September 2011. The gaseous source is a technical challenge and therefore has been divided into two components. The “demonstrator” consists of the inner chamber of the source along with the cooling system used to maintain the temperature of the source to ±30 mK. The demonstrator was delivered to KIT in October 2010 and has passed all its acceptance tests and is being shipped back to the manufacturer to be mated to the magnet system. The magnet system now sets the critical path for the project. The system consists of five, 3-T superconducting solenoids along the bore of the source and two pairs of magnet dipoles at each end that are used to steer a diagnostic electron beam down the source. 1.2.1 Status of the U. S. contribution to the KATRIN experiment P. J. Doe The University of Washington was among the founding institutes that submitted a Letter of Intent in September 2001 with the goal of reaching a sensitivity of 350 meV. The response to


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    UW CENPA Annual Report 2010-2011 April 2011 5 the LoI was to request an improvement in sensitivity. In February 2005 this request resulted in a design report with an improved sensitivity of 200 meV. At this time the Massachusetts Institute of Technology joined the US effort. In June 2007 funds were awarded by the DOE Office of Nuclear Physics to support construction of the KATRIN detector system and devel- opment of the data acquisition system. Additional US institutes involved in KATRIN include University of North Carolina, Chapel Hill (2008), the University of California Santa Barbara (2009) and the Lawrence Berkeley National Laboratory (2009). In addition to the detector task (led by UW) and the DAQ task (led by UNC), the US is also involved in the simulations task (led by MIT), the design of the rear calibration system (UCSB participation) and the US analysis program (led by LBNL). Only the status of the detector task is covered here. In August 2007 a formal design review of the detector system determined that the design was compatible with the KATRIN system and would satisfy the physics goals, allowing the acquisition of long lead items to begin. The principal components of the design are shown in Fig. 1.2.1-1 -53+%$9&:3*0$ !*0*+0.'$9&:3*0$ 456*'$.72+$('58*'$6.&'(/$ -./0$&++*1*'&2.3$'&+,$ ;&+<<9$/=/0*9$ ;*0.$&3($/%5*1($ !"#$%&'()&'*$'&+,$ Figure 1.2.1-1. A schematic view of the KATRIN detector system showing the principal components. The detector system contains two warm-bore solenoid magnets. The pinch magnet defines the highest magnetic field in the whole magnet train. Nominal fields of the pinch and detector magnets are 6 T and 3.4 T respectively. The magnets are operated in the persistent mode and are cooled using helium reliquefiers. The 10-cm diameter detector wafer is located on-axis at the center of the detector magnet bore. To be compatible with the extreme vacuum of the


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    6 main spectrometer, a vacuum of better than 10−9 mbar is required in the detector chamber. To optimize performance while not degrading the vacuum, the preamplifiers are located in a separate vacuum chamber immediately behind the detector wafer operated at a pressure of better than 10−6 mbar. All vacua are maintained by vibration isolated cryopumps. To reduce thermal noise the detector and preamplifiers are cooled using a pulse tube cooler. Given the low end-point energy of the beta decay, intrinsic backgrounds are a concern. To reduce detector backgrounds, all materials in close proximity to the detector are chosen for low radioactivity, including the use of ceramic circuit boards for the preamplifiers. In addition the detector vacuum chamber is surrounded by 3 cm of lead, 1 cm of copper and a plastic scintillator veto. Furthermore, up to 30 kV post acceleration can be applied to the decay electrons to further raise the signal above the low energy backgrounds. Since the outputs of the preamplifiers may float at up to 30 kV, fiber optic drivers/receivers are used to pipe the signal to the data acquisition hardware which also receives signals from the veto system. The front-end electronics and DAQ hardware is supplied and maintained by KIT. The DAQ hardware is derived from the system developed for the Auger cosmic ray experiment and is under control of the ORCA software derived from the SNO experiment and maintained by UNC. All vital signs, temperatures, pressures, voltages, etc. are recorded by a slow controls system provided and maintained by KIT. A figure of merit has been defined based on fundamental detector performance parameters such as energy resolution and backgrounds that will be used to determine if the detector system is capable of meeting its physics goals. Table 1.2.1-1 shows minimum required values for the principal parameters along with the engineering design goals for that parameter. In the following section progress to meeting those goals during detector commissioning is described. Parameter Minimum Eng. Design Units F 1.2 1.1 - s - 1 kev (σ) bd - 0.4 mHz/keV Area 63 80 cm2 Spatial res. 20 20 pixels/detector dia. Time res. 212 45 ns (σ) Muon eff. - 95 % Post acc. 1 30 kV Table 1.2.1-1. The minimum and engineering design performance specifications. The figure of merit, F, is an overall measure of the detector performance, s the detector resolution and bd is the detector background. 1.2.2 Commissioning the KATRIN detector P. J. Doe The KATRIN detector system is currently in the commissioning phase during which the detector subsystems are exercised to determine whether they satisfy the performance criteria


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    UW CENPA Annual Report 2010-2011 April 2011 7 given in the detector design report and the minimum performance required to ensure that the physics goals can be achieved. The status of commissioning these subsystems is given below. 1.2.2.1 Commissioning the detector and electronics B. L. Wall Commissioning of the focal plane detector (FPD) and electronics is currently underway. The front-end electronics chain has been installed into the detector section vacuum system and connected to the DAQ via the fiber optic chain. The FPD and electronics have been operated at high voltage in conjunction with the post-acceleration electrode (PAE). The basic detector system characteristics, including the timing resolution, γ and electron energy response, and an initial estimate of the background have been determined. The testing of the detector electronics at high voltage was carried out in two phases. In the initial phase the number of front-end electronics channels was reduced to 12. During this phase, the system was elevated to 20 kV. High voltage discharges in this phase damaged most of the preamplifiers in the vacuum. Transient suppression was added to the front-end electronics and other peripheral hardware to protect against discharges. The electronics have been operated at 10 kV for 24 hours without damage due to high voltage discharge. Figure 1.2.2.1-1. The focal plane detector energy response to electrons. Initial tests of the FPD and electronics showed the γ resolution to be 1.67 ± 0.03 keV (FWHM). A major contributor to the resolution was microphonic impulse noise from the two vacuum cryopumps. Isolating the cryopumps with a set of bellows improved the γ resolution by 10% to 1.50 ± 0.03 keV. The FPD’s electron energy response is shown in Fig. 1.2.2.1-1. The energy resolution for 18.6-keV electrons is 1.60 ± 0.02 keV.


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    8 A single pixel background rate of 17.1 ± 0.6 mHz was obtained for a region of interest of 16.6 to 20.6 keV. This is above the background goal of 1 mHz, but the data were taken with an incomplete shield and without the veto system. Many events were found to be correlated with high energy events from other channels. A timing cut on high energy events and the use of the veto system should significantly reduce the background rate. The system timing resolution was determined to be less than 127 ns. It was measured by pulsing the photo-electron calibration source in sequence with an external sync pulse input to the data acquisition crate. Individual components of the system are capable of better performance and further tests are planned to look into contributions to the 127 ns. The current measured resolution, however, surpasses the detector specification of 212 ns. 1.2.2.2 Status of the magnets L. I. Bodine The superconducting magnets of the KATRIN detector section were commissioned at the University of Washington (UW) in February, 2010. They have been successfully ramped four times to the nominal field values of 3.6 T at the center of the detector magnet and 6 T at the center of the pinch magnet. They have also been ramped to lower field values for testing detector section components. Slow controls monitoring of the magnets was modified to use the RS-232 protocol resulting in improved robustness of remote magnet monitoring. In addition, the helium recondenser system was upgraded to allow recording and remote monitoring of the pressure inside each cryostat. In February, 2011, during a ramp of the magnet pair the pinch magnet quenched at 6 T. A vacuum leak into the cryostat has been identified as a possible cause. Cryomagnetics, Inc. will attempt to fix the leak in situ at the end of March, 2011. The detector magnet will remain at UW while the pinch magnet is repaired so that the complete magnet system can be tested in April, 2011. 1.2.2.3 Status of the vacuum system J. F. Amsbaugh The KATRIN focal plane detector (FPD) vacuum system is comprised of two systems; the extreme high vacuum (XHV) and the high vacuum (HVac). The XHV system supports the γ and electron calibration sources and the post acceleration electrode (PAE), on the end of which the FPD is mounted. The HVac system surrounds the PAE component of the XHV system where it extends into the magnet bore. The HVac provides thermal isolation. Cooling for the detector and electronics is provided by a pulse tube cooler. Both system vacua are maintained by cyropumps and are pumped down from atmospheric pressure with two turbo-molecular pump systems which can also provide bakeout pumping.


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    UW CENPA Annual Report 2010-2011 April 2011 9 As reported before1 , the XHV system achieved 1.5 × 10−9 mbar with all components at room temperature and after a 120◦ C to 135◦ C bakeout. Testing the PAE assembly after vacuum brazing revealed that the PAE assembly had permanently deformed by about 1 cm. After several pump out and vent cycles the creep rate stabilized and we decided to continue our commissioning tests with this PAE. A redesigned version of the PAE is currently being manufactured. The measured displacement of the new PAE under vacuum loading is 0.011 ± 0.0005 inches, consistent with FEA estimates. The vacuum systems have been vented, disassembled, reconfigured, and pumped out eight times in the last year as commissioning and testing have progressed. Typical XHV vacua prior to venting range from 2 to 3 × 10−9 mbar without the FPD assembly installed and 5 × 10−9 mbar with the FPD installed. All of these measurements had detector cooling present. The FPD cooling tests indicate that improvements in the cooling are needed. The current hard copper connection to the pulse tube cooler is being replaced with a higher efficiency thermo-siphon. The testing of the PAE voltage with a magnetic field present and a faraday cup in place of the FPD caused erosion and failure of the plated aluminum electrodes on the quartz tubes. These have been replaced by thin, stainless steel sheet and the electrical connection was improved. The as-delivered faulty vacuum gauge and controller have been repaired. Temporary bellows couplings were installed on both cryopumps and were found to be be very effective in reducing microphonics noise. Permanent edge welded bellows assemblies have been ordered that will not reduce the cryopump’s effective pumping speed as much as the temporary ones. 1.2.2.4 Status of the calibration system E. L. Martin The electron source uses a titanium disc biased at high voltage and illuminated with a UV LED. The current from the electron source is measured by a precision current meter attached to the disc (PULCINELLA.) The γ source uses a radioactive isotope placed inside an aluminum tube. Both sources use pneumatic motor driven linear actuators to move the source in and out of the beam line. Both sources have been demonstrated suitable for detector calibration. Source movement as well as electron source voltage control have been successfully integrated with slow controls. The γ source currently uses an Am-241 source. A Cd-109 source will also be used but has not yet been purchased due to the short life time. The γ source has been used to determine detector resolution by the width of the 56-keV Am-241 γ emission. PULCINELLA has been installed in the detector and significant noise was discovered at high voltage due to mechanical vibration changing the capacitance of the electron source disc. Accuracy is expected to scale in proportion to electron source potential and be 1.7 pA/Hz at 18.6 kV, allowing absolute detection efficiency to be determined to 3% in one hour from 1 CENPA Annual Report, University of Washington (2010) p. 5.


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    10 a detector rate of 10 MHz. The electron source has been used to determine detector timing resolution by pulsing the electron source. A flood illumination device has been combined with the electron source illumination device for testing the linearity of the focal plane detector and electronics. Illumination is provided by a red LED stabilized by feedback from a pin-diode to produce light with intensity proportional to the input voltage. Testing is underway to determine if this will be sufficient. 1.2.2.5 Status of the veto E. L. Martin The veto uses six scintillator panels surrounding the lead and copper passive detector shield. Light from the scintillators are read out by wavelength shifting fibers and silicon photomulti- pliers (SiPMs.) The SiPM signals are read out by the detector DAQ system and coincidence between SiPM signals is used to detect the passing of a muon. The SiPMs used for veto panel readout have been replaced with a different model allowing the readout fibers to be placed closer to the SiPM active surface. This resulted in improved detection efficiency due to less light loss. In addition a new trigger scheme requiring both a coincidence of individual readout fibers on a veto panel as well as a threshold on the sum of all fibers on the panel has been implemented to reduce noise. Combined with cooling the SiPMs using a Peltier cooling device to further reduce noise to allow lower thresholds without significant deadtime, the veto is expected to meet the design detection efficiency of 95%. The passive shield and veto panels have been installed around the detector vacuum system. The veto signal summing boards and the new cooling box are still being constructed and tested. The veto DAQ firmware is still under development but the DAQ system can be operated using a focal plane detector readout mode to read out the veto signals. The system is expected to be installed in the detector and tested in February, 2011. 1.2.2.6 Status of the DAQ and slow controls M. A. Howe∗ The KATRIN version 4 first and second level trigger (FLT and SLT) electronics were built at Karlsruhe Institute of Technology (KIT) and delivered to the University of North Carolina (UNC) for testing. After ORCA support for the SLT and FLT cards was completed and verified, the electronics were shipped to UW to be used in the final commissioning of the KATRIN focal plane detector (FPD) and cosmic-ray veto system. For the FPD, the KATRIN DAQ electronics uses a trapezoidal filter to detect and record energy information from the detector pixels. In order to verify the function of the FPGA ∗ University of North Carolina, Chapel Hill, NC.


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    UW CENPA Annual Report 2010-2011 April 2011 11 coded filter, a software version of the filter was developed. The results of both filters were compared and it turned out that there was a malfunction of the FPGA filter, which created a random shift of the calculated energy values at each run start. After a revision of the FPGA code at KIT, a comparison with the software filter showed that the FPGA filter is now working correctly. The DAQ system has been collecting commissioning data and assisting in commissioning the FPD detector and electronics. A new version of the FLT FPGA firmware was developed at KIT to support the KA- TRIN veto system as a run-time option. This allows one IPE crate to support both veto and the FPGA readout modes simultaneously. The ORCA FLT support software was ex- panded to support the new veto parameters. The veto configuration of the FPGA firmware has undergone verification at the University of Washington (UW), UNC and KIT. The task of verification included the analysis of output from pulser, scintillator and silicon photomul- tiplier (SiPM) electronics analogous to the configuration intended for use in the KATRIN experiment. During this testing, synchronization issues within the system’s readout and problems with dropped events were observed. These problems require a subsequent redesign of the FPGA code at KIT, which is currently underway. The ZEUS slow control system was installed at UW to monitor the KATRIN magnet temperatures, power supplies, cryogen levels, and other parameters. All of the slow control parameters are inserted into an ADEI database (also running at UW). ORCA can link to the ADEI database and use selected parameters in its slow control subsystem where users can set up custom monitoring and alarms. A number of new features were added to the ORCA slow control subsystem. It now auto-starts with ORCA, email reports can be sent upon process start and stop, heartbeat emails can be sent, and a confirmation alert is posted if a user tries to stop ORCA while a slow control process is running. In addition, a high-level display was added to optionally hide the complex low-level slow control set up display. Several ORCA systems are being used in production running to monitor the conditions during the commissioning. A major upgrade of the slow control for the KATRIN Detector system has been carried out. The field point program has been migrated and adapted to a new, more powerful, field point controller, the National Instruments cFP-2220. An additional digital input module has been added to the slow control system hardware to monitor the vacuum valve outputs. This allows monitoring the interlock and/or fuse status of the vacuum system valves. A new GUI slow control interface program has been developed and installed on the new ZEUS PC. It is a web-based application that can be remotely interfaced from a web browser providing full control and monitoring of the detector slow control systems. 1.2.2.7 Near-time analysis tools S. Enomoto A set of software tools has been developed for the on-going KATRIN detector commission- ing at the University of Washington (UW) and forthcoming detector and main spectrometer


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    12 commissioning at Karlsruhe Institute of Technology (KIT). The tools were designed for the rapidly progressing commissioning phase, where quick analysis investigations by on-site peo- ple are crucial for timely trouble shooting and performance evaluation, while predictions of what will be necessary are generally difficult. Due to the heuristic nature of commissioning activities, it is quite common that people are inclined to write application-specific one-time- use quick-and-dirty programs. Although such programs are intended for single use, they are a logical record of the investigation activities and experiences, and if accumulated properly, they will be a valuable knowledge base at later stages. The KATRIN near-time analysis tools were designed with these things in mind: they are designed to be adaptive to unexpected applications, to be quickly applicable to specific purposes by end-users, and to make all investigation outcomes reusable and traceable. Two different types of tools are provided: interactive and batch-oriented (Fig. 1.2.2.7-1). Figure 1.2.2.7-1. Left: Interactive tool, with user FPD pixel view plugin and user waveform plugin. Right: Automation tool, used for detector commissioning processing and analysis. The interactive tool serves to co-ordinate analysis logic, data, and human operation. Analysis logic is implemented by runtime user plug ins. The tool is solely written with ROOT without any external libraries, thus a user ROOT program can be directly used as an analysis plug in. One typical application of the tool is as an event browser with runtime choice of user analyzers. There are also plans to use it for the main spectrometer and detector system. The batch-oriented tool automates any type of routine processing and summarizes the processing status and results. It automatically solves dependencies for chained processing. It automatically recognizes data content, classifies the data, and then determines which processor to execute. It can run any user executable according to a user configuration written in XML and the output from the user executable is traced by the tool. The status and results can be accessed with RESTful Web APIs, interfacing web browsers, and user programs. For the on-going detector commissioning at UW, several data analyzers are setup for automatic execution among other automated processing such as format conversion (from ORCA files to ROOT objects) and slow-control data extraction (ADEI interface).


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    UW CENPA Annual Report 2010-2011 April 2011 13 MAJORANA 1.3 MAJORANA DEMONSTRATOR Activities J. F. Amsbaugh, T. H. Burritt, J. Diaz Leon, P. J. Doe, G. C. Harper, M. A. Howe∗ , R. A. Johnson† , M. G. Marino‡ , M. L. Miller, D. A. Peterson, R. G. H. Robertson, A. G. Schubert, T. D. Van Wechel, J. F. Wilkerson∗ , D. I. Will, and B. A. Wolfe The MAJORANA Collaboration is performing R&D to demonstrate the feasibility of building a 1-tonne modular array of 86% enriched 76 Ge capable of searching for neutrinoless double- beta (0νββ) decay in the inverted mass hierarchy region (∼30 meV). A cornerstone of the plan is the development and construction of the MAJORANA DEMONSTRATOR, a R&D mod- ule comprised of 30 kg of 86% enriched 76 Ge and 30 kg of non-enriched Ge detectors. The use of a mixture of both enriched and natural or depleted Ge, has the advantages of lower- ing the costs in the R&D phase, accelerating the deployment schedule, and also giving the MAJORANA DEMONSTRATOR an opportunity to verify that any observed peak in the 0νββ region of interest is directly associated with the presence of 76 Ge. The broad goals for the DEMONSTRATOR are: • Show that backgrounds, at or below 1 count/ton/year in the 0νββ - decay peak 4-keV region of interest, can be achieved, a necessary condition for scaling to a 1-tonne or larger mass detector. • Demonstrate sensitivity by testing the validity of the Klapdor-Kleingrothaus reported 76 Ge 0νββ observation1 . • Show successful long-term operation of crystals in their respective environments. • Demonstrate a cost-effective and scalable approach. The proposed method uses the well-established technique of searching for 0νββ in high- purity Ge (HPGe) diode radiation detectors that play both roles of source and detector. These detectors will be located in specially fabricated ultra low-background, electroformed Cu cryostats. The technique is augmented with recent improvements in signal processing, detector design, and advances in controlling intrinsic and external backgrounds. Major ad- vances in detector R&D (both laboratory and industrial) have lead to the choice of p-type point-contact (PPC) detectors for the demonstrator module. These detectors offer low capac- itance and excellent resolution, providing the ability to (1) tag and veto two-site background interactions via pulse shape analysis and (2) probe ultra low-energy events (E>∼300 eV) to competitively search for dark matter candidates (WIMPs, axions, etc)2 . Project execution of the MAJORANA DEMONSTRATOR is currently underway at full steam. Items on the overall project critical path are addressed below: ∗ University of North Carolina, Chapel Hill, NC. † University of Colorado, Boulder, CO. ‡ Excellence Cluster Universe, Munich, Germany. 1 H. V. Klapdor-Kleingrothaus, I. V. Krivosheina, A. Dietz, and O. Chkvorets, Phys. Lett. B 586, 198 (2004). 2 C.E. Alseth et al., http://arxiv.org/abs/1002.4703.


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    14 • Funding. The MAJORANA DEMONSTRATOR project passed the major DOE CD1 review in 2010 and is preparing for CD2 review in 2011. • Host Lab. The 4850 ft laboratory at Sanford Underground Laboratory (SUL) is nearly ready for beneficial occupancy. • Electroforming. Copper growth has begun in earnest at a temporary underground cleanroom at SUL as well as PNNL. • Detector Procurement. The natural germanium detectors have been purchased and are stored underground at SUL, and we are preparing to procure enriched germanium in 2011. The MAJORANA group at the University of Washington is playing a leading role on many levels including project management, software and computing, technical R&D, engineering, and fabrication: • Project Management. Robertson continues to serve as a member of the MAJORANA governing board (SAC) and Miller is deputy task leader for the module task • Software and computing. Holman maintains the core collaborative tools (wiki, calendar and wiki) on virtualized UW servers as well as exposing the Athena computing cluster for general MAJORANA simulations and data analysis. Miller is designing and imple- menting the data management and workflow management tools for the collaboration. • Simulation and analysis. Schubert continues to develop tools to describe, simulate and validate our understanding of radioactive backgrounds in both the MAJORANA DEMON- STRATOR as well as prototype detectors (e.g. MALBEK) • Host lab infrastructure. Diaz and Will have nearly completed major effort to extract, package and ship 40 tons of old lead that was previously used in an early radio carbon dating experiment at UW. This lead is highly valuable due to its low radioactivity and will form the inner shield of the MAJORANA DEMONSTRATOR. • Detector R&D. We are involved on many fronts. Knecht and Miller are leading the design, fabrication and testing of ultra low-background parylene cables and connectors for both the detector signals and high voltage. Leon is performing additional character- ization of PPC detectors as well as testing, evaluation and commissioning of digitizers. Robertson is leading design, fabrication and testing of a highly innovative preamplifier design for ultra-low noise. Miller is leading the effort to validate long-term operation and stability of a PPC detector (CoGeNT) with an emphasis on the low-energy spec- trum for cosmogenic background identification and suppression as well as opportunistic Dark Matter searches. • Engineering. Burritt remains an invaluable resource for design and fabrication of innu- merable key components, including the tooling for parylene fabrication, detector mounts into strings, the thermosyphon and cryostat. Harper has led the design and fabrication of multiple cryostats for string testing and storage underground.


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    UW CENPA Annual Report 2010-2011 April 2011 15 In the following articles we briefly highlight selected accomplishments in the past year. 1.3.1 A Monte-Carlo model of the background energy spectrum of the MALBEK detector J. I. Collar∗ , P. S. Finnerty† , G. K. Giovanetti† , R. Henning† , M L. Miller, A. G. Schubert, and J. F. Wilkerson† A good understanding of the MAJORANA DEMONSTRATOR background energy spectrum will be required to project background rates for a tonne-scale germanium experiment and to interpret results of a neutrinoless double-beta decay search. A modified CANBERRA Broad-Energy germanium (BEGe) detector has been deployed in a low-background shielded environment at the Kimballton Underground Research Facility (KURF), in Ripplemead, VA. This detector, the MAJORANA Low-background BEGe at KURF (MALBEK), provides an opportunity to study the background energy spectrum of a well-understood low-background germanium detector. Studies of the MALBEK detector and simulations of detector response to background radiation can be used to inform a background energy spectrum model for the MAJORANA DEMONSTRATOR. 103 counts / keV 102 10 1 0 500 1000 1500 2000 2500 Energy [keV] Figure 1.3.1-1. A background energy spectrum collected from the MALBEK detector in September through November of 2010; 56 days of live time. A model of the MALBEK detector has been created in MaGe, a physics simulation soft- ware package jointly developed by the MAJORANA and Gerda collaborations. MaGe was used to simulate the response of the MALBEK detector to decays of naturally-occurring ra- dioactive contaminants in the MALBEK cryostat and shield. Results of these simulations are combined with information on material radiopurity to create a model of the MALBEK back- ground energy spectrum. This model can be compared to the spectrum collected at KURF ∗ Kavli Institute for Cosmological Physics and Enrico Fermi Institute, University of Chicago, Chicago, IL. † University of North Carolina, Chapel Hill, NC, USA and Triangle Universities Nuclear Laboratory, Durham, NC.


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    16 to verify understanding of backgrounds and the performance of the simulation software. A background energy spectrum collected from KURF appears in Fig. 1.3.1-1. 1.3.2 Pre-amplifier with forward biased reset for MAJORANA D. A. Peterson, R. G. H. Robertson, and T. D. Van Wechel Development continues on a charge sensitive pre-amplifier which is continuously reset by the forward biased gate to source junction of the input JFET. The DC stabilization of a conventional charge sensitive amplifier is provided by a high-value feedback resistor in parallel with the feedback capacitor. This resistor provides a DC path for the net input bias and detector currents at the amplifier input, so that the feedback capacitor does not eventually charge to the output saturation voltage. It would be advantageous to eliminate the feedback resistor as it is a major noise source. It is possible to operate a JFET with zero volts on the gate, or even a small forward bias. A JFET has an operating point where the current of the forward biased gate cancels the reverse leakage current. The detector leakage of a positive biased detector can also be cancelled. A feedback resistor is not required when the JFET operates with the gate open eliminating its noise contribution. Charge feedback can still be applied to the gate through a feedback capacitor. Some other means is needed to stabilize the DC operating point. We are using a tetrode JFET that has superior noise performance and provides a means of DC stabilization without a DC connection to the gate. A tetrode JFET has two gates: – the control gate has small capacitance for improved performance, while the substrate gate can be used to set the drain-source current IDS . There are two feedback loops, one operating at high frequencies, which provides charge feedback to the control gate. The other, low-pass, loop is connected to the substrate gate, stabilizing the DC operating point so that the average net charge at the input is zero. The pre-amplifier transfer function is affected by the two low-frequency corners in the feedback paths. One is that of the low pass loop for the stabilization of the DC operating point. The other low frequency corner is that of the high-pass charge loop, which depends on the dynamic resistance at the JFET control gate and the input capacitance (detector, gate and feedback). The dynamic input resistance seen at the gate is inversely proportional to the gate current and is on the order of 25 GΩ at a gate current of 1 pA at room temperature. As a result, the low-frequency corner of the charge loop is proportional to detector leakage current. Above the corner of the low-pass loop the feedback phase lags by 90◦ and below the corner of the high-pass loop it leads by 90◦ . If the corner frequency of the low-pass loop is lower than that of the high pass loop, the total feedback at the intersection vanishes because of their relative phases. The amplifier output will be large and noisy near that frequency, as we found experimentally with the prototype pre-amplifier, which had excessive low frequency noise. We learned that the low frequency corner of the low pass loop needs to be set above that of the low frequency corner determined by the highest operational detector current. The output noise level of our prototypes has been higher than predicted by circuit simu-


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    UW CENPA Annual Report 2010-2011 April 2011 17 lation. It is now believed that the bipolar transistors on the HFA3096 transistor array that we are using, have excessive noise at low frequencies. Recent measurements show that when a diode connected transistor that biases the base of the cascode transistor was replaced with a conventional diode, that the series noise voltage decreased by more than 20%. We are now constructing a new prototype with discrete transistors to see if there is an improvement in the output noise. The cascode amplifier stage was also improved. Circuit simulation showed that the impedance looking into the emitter of the cascode transistor was much higher than it should be. The output of the cascode drives a bootstrapped voltage follower stage with a very high effective input impedance which is partially reflected back to the cascode input. This was solved by stacking two cascode transistors in series. Originally less than half the JFET ac drain current was coupled into the emitter of the cascode transistor. Now more than 95% of the ac drain signal is coupled into the cascode. 1.3.3 Digitizer evaluation with PPCII J. Diaz Leon, A. Knecht, and M. L. Miller A critical element of the MAJORANA data acquisition system is the analog-to-digital con- verter, which allows for the fast triggering and digitization of pulses from germanium de- tectors. Several digitizer cards have been tested for compatibility with the needs of the MAJORANA collaboration1 , and currently the Struck SIS33022 digitizer is being evaluated. Signals from PPCII3 , a P-type point-contact germanium detector, have been used for this purpose and this setup has also proven to be invaluable for testing analysis software. ch0_dec2_FirstInternalClock htemp ch0_dec2_SecondInternalClock htemp Entries 2403200 3 Entries 2402400 ×10 Mean 0.001812 Mean -0.05021 80000 RMS 9.33 120 RMS 4.335 70000 100 60000 80 50000 40000 60 30000 40 20000 20 10000 0 0 -30 -20 -10 0 10 20 30 -20 -10 0 10 20 Adc-Baseline Adc-Baseline Figure 1.3.3-1. Distribution of ADC value about the waveform baseline using the first internal clock (left) and the second internal clock (right). A wider distribution corresponds to a noisier waveform. Each digitized waveform of the PPCII preamp consists of up to 65536 (16-bit width) samples at 100 MS/s. The energy and timing parameters obtained from these waveforms 1 CENPA Annual Report, University of Washington (2010) p. 18. 2 Struck Innovative Systeme, www.struck.de. 3 On loan from John Orrell, Pacific Northwest National Laboratory, Richland, WA.


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    18 can be used to determine the location and nature of the interaction which caused them. Furthermore, analysis of the digitized waveform’s shape is used to distinguish multi-site vs. single-site interactions, which is relevant for suppression of backgrounds (e.g. γs from thorium series). Efforts were made to characterize the electronic noise of the system which revealed some undesirable behavior from one of the digitizer card’s internal clocks. Jitter generated by the DLL/PLL of the card’s FPGAs every other clock edge manifests itself as extra noise in the waveforms. Use of the other internal clock in the card corrects this (see Fig. 1.3.3-1), an example of valuable progress made with this system. A recent firmware upgrade of the SIS3302 aimed at extending the card’s ability to collect longer pre-trigger data, which would improve triggering at low amplitudes, will be tested at CENPA with this setup. This entails measurements of the digitizer dead-time, low energy threshold and triggering efficiency, and optimization of online triggering parameters. In addition, by scanning a source along the detector it is possible to measure its response to position dependent interactions, i.e. how waveform rise-time distribution depends on the location of the interaction. 1.3.4 Design, fabrication and testing of HV and signal cables and connectors for the MAJORANA experiment N. M. Boyd, T. H. Burritt, A. Knecht, M. L. Miller, D. A. Peterson, R. G. H. Robertson, and B. A. Wolfe We have produced several prototype parylene cables using the apparatus and methods de- scribed in last year’s report1 . For the first time, we produced a full cable in our class-1000 clean room (see Fig. 1.3.4-1) in order to meet the low radioactivity requirements. Initial results were ∼ 3 times higher than expected. We are currently investigating the source of a possible contamination and refining our vacuum system. In addition to the signal parylene cables we started to produce a high voltage compatible cable. We chose a 25-mil copper wire with 3 mils of parylene coating in order to withstand nearly 10 kV without breakdown. Due to its larger diameter we were able to hang the cable directly into the coating machine instead of working with a mandrel and thus were able to apply the 3 mil parylene coating in one pass. After the parylene coating we used our sputter source to deposit 100 nm of copper onto the outside of the parylene thereby producing a shielded coaxial cable. As the cable withstands the required voltage without breakdown, we are currently investigating its microdischarging properties. In addition to the actual cables we started designing connectors which will be mounted onto the cold plate directly above the germanium detectors. These will allow for easier installation of the detectors without having to route the appropriate cables all the way out of the shielding to the electronics. However, this means that we need to meet stringent background requirements which severely constrain the choice of materials thus excluding any commercial solutions. 1 CENPA Annual Report, University of Washington (2010) p. 24.


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    UW CENPA Annual Report 2010-2011 April 2011 19 For the signal cable, we chose boards made of fused silica which are coated with gold traces. The copper wires of the signal cable are wedge bonded onto those gold traces and the two boards are pressed together such that the gold traces make contact. We then assemble the boards for a total of 5 cable connections in a copper garage (see Fig. 1.3.4-1) for testing. Figure 1.3.4-1. Left: Microscopic picture of our produced 10-wire parylene cable. The wires have a diameter of 3 mils and are separated by 6 mils. Right: Connector “garage” to connect five signal cables. The size of the garage is approximately 30 × 20 × 10 mm3 . The high voltage cable connector is based on a PTFE block into which the cables are inserted. For the actual connection of the two bare high voltage leads we are currently finalizing two designs based on either clamping or crimping scenarios. 1.3.5 Searches for dark matter with a MAJORANA prototype J. I. Collar∗ , A. Knecht, M. G. Marino† , M. L. Miller, J. L. Orrell‡ , and J. F. Wilkerson§ Since the end of 2009 we have been operating a low background P-type point contact (PPC) germanium detector at the Soudan Underground Laboratory in Soudan, MN. This detector exhibits low noise allowing for a very low threshold (below 0.5 keV). Due to this low thresh- old, the detector is very sensitive to low-mass WIMPs despite its small mass (0.5 kg) and is sensitive to a new region of parameter space. The setup at Soudan has been described in last year’s report1 . The data from the first 50 days have been published2 while the data from the first 150 days served as the basis of M. Marino’s thesis3 . Over the course of the last year the detector was continuously running underground without any modification. That amount of data will allow us to search for an annually modulated dark matter signal, a sensitive test of the WIMP hypothesis. In order not to bias ∗ University of Chicago, Chicago, IL. † Excellence Cluster Universe, Munich, Germany. ‡ Pacific Northwest National Laboratory, Richland, WA. § University of North Carolina, Chapel Hill, NC. 1 CENPA Annual Report, University of Washington (2010) p. 19. 2 Aalseth et al., arXiv:1002.4703v2. 3 M. G. Marino, Ph. D. thesis University of Washington (2010).


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    20 our data quality cuts and selections towards an annual modulation, we devised a doubly-blind method by randomly redistributing the day of the event and suppressing the actual time of exposure. 200 Events / ( 0.05 keV ) 180 160 140 120 100 80 60 40 20 2 4 6 8 10 12 Energy (keV) Figure 1.3.5-1. “High energy” spectrum for the first full year of data collection. The goal for the analysis is to finalize the cuts and selection criteria on the blinded data before moving on to the actual modulation analysis and hypothesis testing. The biggest challenge of the analysis will be to correctly take into account the several background peaks present in the spectrum (see Fig. 1.3.5-1), their decaying amplitudes, and their contributions to the flat background. 1.3.6 Data management and workflow management for the MAJORANA DEMONSTRATOR B. A. Wolfe, M. G. Marino∗ , M. L. Miller The MAJORANA DEMONSTRATOR experiment is targeted squarely at scaling the deployment of enriched 76 Ge detectors from the well established scale of 1-10 kg to 100 kg and, ultimately, up to 1 tonne. A major challenge in this enterprise is the automation of the data management and processing workflow management (DMWM). In the following we briefly highlight the design of a prototype DMWM system for the MAJORANA DEMONSTRATOR, lessons learned from continued operation with the prototype detector systems at Soudan, and the anticipated design for a system that scales to support 1 tonne of detectors. The MAJORANA DEMONSTRATOR will consist of 105 BEGe detectors, each having a low- and high-energy channel to span the energy range from ∼300 eV to 10 MeV. A parallel DAQ system powered by ORCA has been field tested at Soudan. The DAQ system generates data files in the ORCA binary format. These (“Tier-1”) files are buffered underground, transferred via the WAN to CENPA for archival on durable storage, and converted to ROOT format (“Tier-2”) for further processing. The ROOT files are next passed through iterative series of ∗ Excellence Cluster Universe, Munich, Germany.


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    UW CENPA Annual Report 2010-2011 April 2011 21 processing applications to create the MGDO encapsulation (“Tier-3”) of event information (energy, timing, wave form data, etc). Finally, a series of flyweight analysis trees (“Tier-4”) suitable for final analysis and publication are skimmed from the MGDO objects and published to a common cloud repository (Dropbox) for consumption by the entire collaboration. Every step in this process, including automated handling of calibration, run selection, etc., is fully automated and provenance tracked in the CouchDB database system that drives a custom python based workflow management package. A prototype system was developed in Spring 2009 and deployed in Summer 2009 for DMWM of the Soudan prototype. It has been running reliably and efficiently for nearly a year and has managed data from three separate detectors installed at various times in Soudan. Additionally, we have developed tools for managing simulation workflow and cataloging and indexing all forms of simulation output at the PDSF computing facility. This system has been tested extensively for intermediate simulation studies and will be used for the upcoming MAJORANA DEMONSTRATOR simulation campaign in preparation for DOE CD2 considera- tion. Finally, we have also developed software and tools to make the MAJORANA DEMON- STRATOR software environment and data files secure and available for authenticated collabo- rators on the Amazon Web Services cloud. This has proven invaluable for overflow computing during the past year’s research and development phase. SNO+ 1.4 Overview of the SNO+ experiment and CENPA’s contribution S. Enomoto, J. Kaspar, J. N. Kofron, D. J. Scislowski, N. R. Tolich, and H. S. Wan Chan Tseung SNO+ is a large-volume underground liquid scintillator neutrino experiment presently under development at the SNOLAB facility, in Sudbury, Ontario, Canada. It is a multi-purpose detector whose reach extends to the following areas of neutrino physics: neutrinoless double beta decay (with Nd-loaded scintillator), geo-neutrinos, reactor and low-energy solar neutri- nos. In addition, a large liquid scintillator detector serves as an excellent supernova neutrino monitor. SNO+ will use a lot of the infrastructure left behind by the completed Sudbury Neutrino Observatory (SNO) experiment, including the acrylic vessel (AV), photomultiplier tubes and most of the electronics. The main engineering work concerns the AV, which will have to be anchored to the floor after scintillator filling. A hold-down system has been designed, and the ropes are now being manufactured. Data-taking is scheduled to start in late 2012. In SNO+ the data rate is expected to be two orders of magnitude higher than in SNO, and therefore updates to the SNO electronics and data acquisition (DAQ) system are needed. CENPA is responsible for updating the DAQ into a faster, ORCA-based system compatible with the electronics upgrades that are being planned by the University of Pennsylvania. These include new XL3 cards for controlling the 19 data crates. Software for operating the


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    22 XL3’s through ORCA has been written and tested at the typical rates expected from SNO+. The full DAQ system will be available for commissioning this year. The status of the DAQ work is described in more detail (see Sec. 1.4.1). CENPA is also responsible for the SNO+ slow control system, which records and monitors a large number of detector-related variables at a rate of ∼1 Hz. Good progress has been made during the past year towards testing and interfacing with the I/O servers that will be used in the slow control system. Data readout and monitoring at the expected rate have been tested for a single I/O server. Work done on the slow control hardware (see Sec. 1.4.2) and software (see Sec. 1.4.3) are described in more detail. The proposed scintillator is linear alkylbenzene (LAB) with ∼3 g/L of 2,5-diphenyloxazole (PPO). To achieve the goals of the experiment, it is imperative to understand the properties of this scintillator. At CENPA, we have an active experimental program geared towards scintillator characterization. Two experiments have been carried out: (1) a test of the electron energy scale linearity of LAB-PPO, which was found to be non-linear below ∼0.5 MeV, and (2) a first measurement of the refractive index of LAB-PPO from 210 to 1000 nm. The test of the electron energy scale linearity of LAB-PPO is described (see Sec. 1.4.4), as well as reports on the dispersion measurement (see Sec. 1.4.5). A third experiment to study Rayleigh scattering in LAB-PPO is currently being developed. 1.4.1 Status of the SNO+ data acquisition software M. A. Howe∗ , J. Kaspar, N. R. Tolich, and J. F. Wilkerson∗ The new DAQ software to handle the data rate expected in SNO+ is based on ORCA: a general purpose, highly modular, object-oriented, acquisition and control system that is easy to use, develop, and maintain. The DAQ pulls data from the VME trigger crate. Nineteen data crates operating in an independent asynchronous way push data into the DAQ system. In 2010, new XL3 controllers for the data crates were developed by the University of Pennsylvania group. They were demonstrated to deliver up to 15 Mb/s of data per single crate—at least 10 times more than the previous generation XL2 controllers could deliver from all the SNO crates together. On the ORCA side, the XL3s are served by circular buffers running in parallel in independent threads. A data manager pulls data from the buffers and serializes them into the data stream to be pushed to an event builder. Fig. 1.4.1-1 shows parts of the user interface to control XL3. A DB specification to replace an unportable old Sun DB was released and is being im- plemented to provide a unified interface to run time parameters for DAQ, MC, slow control, and monitoring tools. The new solution is based on replicated CouchDB servers and all the data are served in JSON format. Two test-stands for DAQ commissioning were in use during this year. A test stand located in Sudbury has been used for most of DAQ development. The second test-stand at Penn was ∗ University of North Carolina, Chapel Hill, NC.


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    UW CENPA Annual Report 2010-2011 April 2011 23 added to debug the new XL3 data crate controller. These test-stands allow us to run both the former SNO DAQ and the present ORCA system in parallel to cross-check the outputs. The agreement between the systems is excellent and the speed improved to 13Mb/sec. Figure 1.4.1-1. A GUI of the new XL3 data crate controller is shown. 1.4.2 Status of the SNO+ slow control hardware readout J. N. Kofron The SNO+ experiment relies on the accurate collection of data from the hardware by the data acquisition system (DAQ). The DAQ must, therefore, be at all times aware of the current state of the hardware, and in particular must have assurances that the hardware is operating within specified tolerances. In order to accomplish this we have developed a slow control system. Conceptually, there are two parts to the slow controls, the low level hardware readout and the high level interface. The low level hardware readout is written in a combination of Erlang and C, and has been completed. The Erlang code passes binary encoded messages to the C code, which interprets them, performs operations on the hardware, and returns data to the Erlang code using another binary message format. These data are then decoded and returned to the requesting process. The system as engineered has been found to perform at a level that is more than adequate for our purposes, and is able to collect data at a rate more than 1000 times that which is necessary. It has also been demonstrated to handle the case of concurrent requests grace- fully, without loss of information. Up to 100 concurrent clients have been tested with no degradation of data or availability. The SNO+ slow control system is therefore complete from the standpoint of hardware readout and is scheduled to be deployed on site at Sudbury, Ontario this year. A test


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    24 deployment is currently in service at CENPA. 1.4.3 Status of the SNO+ slow control software D. J. Scislowski In order to make data acquisition from the SNO+ slow control hardware system portable and accessible to different clients, an HTTP brokerage layer was designed and implemented. It takes requests from any user-end HTTP client, relays them to the native Erlang code running on the IO servers, then parses, formats, and returns any output to the user client. Standard HTTP return codes indicate the success or failure of the request, and attached JSON message bodies contain either the data requested, or details of any errors. Card voltages and configurations can be read with HTTP GET requests, while POST requests allow the user client to change card modes and channel gains by supplying the desired parameters in a JSON data structure. Making use of the widely used Erlang based webmachine1 web framework ensures reliable, fault tolerant communication to the hardware layers, and a high performance under many operating conditions. 1.4.4 The electron energy scale linearity of SNO+ scintillator N. R. Tolich and H. S. Wan Chan Tseung It is commonly assumed that the response of a liquid scintillator (LS) to e− is linear except at very low energies, where ionization quenching becomes significant. However, there have been some reports from the KamLAND collaboration that the observed non-linearity of the e− energy scale in their LS cannot be solely described by Birks’ law2 . It was suggested that there is a contribution from Cherenkov UV photons which are absorbed and re-emitted at longer wavelengths. Here, we report on results from an experiment to investigate the e− energy scale linearity of SNO+ LS between 0.075 and 3 MeV. To investigate the e− energy scale of the scintillator LAB-PPO (linear alkylbenzene with ∼3 g/L of 2,5-diphenyloxazole), mono-energetic electrons were produced by the Compton scattering of a collimated γ-ray beam inside an LAB-PPO target coupled to a PMT. The scattering angle of the γ measured with a NaI detector is directly related to the e− energy in the LAB-PPO target by the Compton formula. A Compton scattering event results in a coincidence signal from the NaI and LS target PMTs. γ rays originated from sealed 137 Cs and 60 Co sources as well as the 12 C(p,p′ )12 C reaction. The UW tandem Van de Graaff accelerator supplied a ∼2-µA beam of 5.7-MeV protons onto a 5-mm thick nat C target, producing a high intensity 4.43-MeV γ source. 1 https://bitbucket.org/justin/webmachine. 2 O. Perevozchikov, Search for electron anti-neutrinos from the Sun with KamLAND detector, Ph. D. thesis, The University of Tennessee, Knoxville (2009).


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    UW CENPA Annual Report 2010-2011 April 2011 25 ×103 ADC bin 3 2.5 2 1.5 1 0.5 0 0 0.5 1 1.5 2 2.5 3 Electron energy (MeV) Figure 1.4.4-1. Left: example data. Right: LAB-PPO results with the fitted Cherenkov and scintillation components in blue and red. Fig. 1.4.4-1 (left) shows the spectra of integrated PMT pulses from the LS that are in coincidence with the NaI detector at 6 scattering angles. In Fig. 1.4.4-1 (right) the peak positions, i.e. relative light output, as a function of e− energy for LAB-PPO are shown in black markers. It is seen that the LS response becomes non-linear in the energy region around the Cherenkov threshold. This non-linearity cannot be explained solely by Birks’ model of ionization quenching. The black line is a fit to the data assuming a two-component light model, Cherenkov (blue curve) and scintillation (red line). The relative magnitudes of these two contributions as extracted in this work will be included empirically in the SNO+ Monte Carlo package. Further work is in progress to verify the linearity of the PMT and electronics used in this experiment. 1.4.5 Measurement of the refractive index of SNO+ scintillator N. R. Tolich and H. S. Wan Chan Tseung In SNO+, an accurate knowledge of the scintillator refractive index as a function of wave- length is essential for reconstructing events, optical modeling, and performing reliable cal- culations of the Cherenkov light yield of charged particles. The refractive index of linear alkylbenzene (LAB) has so far been measured at only a few wavelengths in the visible region. Here we report on the first measurement of the refractive index within ±0.005 for both LAB- PPO and Nd-doped LAB-PPO at 500 points in the wavelength range 200–1000 nm using ellipsometry1 . Fig. 1.4.5-1 shows our results for LAB with 3 g PPO/L. The yellow curve is the average refractive index from the five angles while the 1-σ band is shown in red. Also shown between 400 and 650 nm are previous measurements by our collaborators at Queen’s University and Brookhaven National Laboratory, Petresa, and the RENO collaboration2 . The Nd-doped LAB-PPO results agree very closely with those from the undoped sample. 1 R. A. Synowicki et al., J. Vac. Sci. Technol. B 22 (2004) 3450. 2 I. S. Yeo et al., Phys. Scr. 82 (2010) 065706.


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    26 Refractive index 1.75 55 deg 60 deg 65 deg 1.7 70 deg 75 deg UW average UW 1 sigma region 1.65 BNL Queen’s Petresa n20D 1.6 RENO 1.55 1.5 3 1.45 ×10 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Wavelength (nm) Figure 1.4.5-1. Refractive index of LAB-PPO as a function of wavelength. The experimental set-up uses a Woollam M2000 ellipsometer1 . A thin film of liquid scintillator was deposited on a frosted glass slide. A beam of polarized light from a Xe lamp is specularly reflected off the liquid surface undergoing a change of polarization that is characterized by two ellipsometric parameters. These are evaluated by the apparatus and can be directly related to the real and imaginary components of the refractive index. Light that is transmitted into the liquid is diffusely reflected off the frosted glass and does not impact the measurements significantly. Readings were taken at five different angles at room temperature. We first verified the validity of this method with a distilled water sample. Project 8 1.5 Status of the Project 8 neutrino mass measurement prototype L. I. Bodine, R. F. Bradley∗ , P. J. Doe, J. A. Formaggio† , D. L. Furse† , R. A. Johnson‡ , J. Kaspar, M. L. Leber§ , M. L. Miller, B. Monreal§ , M. F. Morales, R. G. H. Robertson, L. J. Rosenberg, G. Rybka, W. A. Terrano, T. Thuemmler¶ , and B. A. VanDevenderk Neutrino mixing experiments indicate the average neutrino mass must be greater than 0.02 eV. The KATRIN experiment has a target neutrino mass sensitivity of 0.2 eV. If the neutrino mass is not within the reach of the KATRIN experiment, it will almost certainly be within ∗ National Radio Astronomy Observatory, Charlottesville, VA. † Massachusetts Institute of Technology, Cambridge, MA. ‡ University of Colorado, Boulder, CO. § University of California, Santa Barbara, Santa Barbara, CA. ¶ Karlsruhe Institute of Technology, Karlsruhe, Germany. k Pacific Northwest National Laboratory, Richland, WA. 1 Access to this equipment was provided by the University of Washington NanoTech User Facility.


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    UW CENPA Annual Report 2010-2011 April 2011 27 the reach of an experiment an order of magnitude more sensitive. The Project 8 group is exploring ideas for a next-generation experiment sensitive to neutrino masses in the 0.02 to 0.2-eV mass range. Even in the event of a null measurement, such an experiment will be able to distinguish between normal and inverted hierarchies of neutrino mass. Figure 1.5-1. Simulation of the signal from an electron trapped in the prototype. Color indicates relative power in receiver. Energy loss from cyclotron radiation is noticeable as an increase in frequency over time. Measuring the frequency of the cyclotron radiation emitted by electrons with tritium endpoint energies in a magnetic field should be able to increase electron energy resolution, and therefore neutrino mass resolution, by an order of magnitude over current experiments1 . We are currently constructing a prototype to detect electron cyclotron radiation and characterize the experimental issues that need to be addressed to scale the method to a neutrino mass experiment. The Project 8 prototype consists of a small magnetic bottle placed into a recently recom- missioned 1-T superconducting magnet with a near-field transmission-line antenna to detect the cyclotron radiation of electrons trapped in the bottle. Electrons will be supplied by 83m Kr, which has been successfully produced using the CENPA tandem accelerator. Because thermal noise will be the primary background to detecting the cyclotron radiation, the entire system will be cooled to roughly 30 K to maximize the signal to noise necessitating a cryo- genic microwave amplifier on loan from NRAO. Simulations indicate the signal from a single electron should be clear, with an energy resolution limited primarily by the uncertainties in the magnetic field as shown in Fig. 1.5-1. 1 B. Monreal and J. Formaggio, Phys. Rev. D 80, 051301, 2009.


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    28 Figure 1.5-2. Partially assembled prototype detector showing the bottle coil (silver), the antenna support (black), and the cryogenic amplifier (gold). Prototype construction (Fig. 1.5-2) is being overseen by visiting graduate student Dan Furse, and is providing excellent hands-on education in cryogenics and RF receivers to a group of three undergraduates (Fig. 1.5-3). Cryogenic tests of the detector are expected to begin early Spring 2011, with electron measurements made by the end of the year. Figure 1.5-3. Project 8 insert construction team posing by the magnet top. Left to right: Gray Rybka, Aaron Stoll (undergraduate), Brynn MacCoy (undergraduate), Lisa McBride (undergraduate), Dan Furse.


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    UW CENPA Annual Report 2010-2011 April 2011 29 HALO 1.6 The HALO supernova detector C. A. Duba∗ , F. Duncan†‡ , J. Farine‡ , A. Habig§ , A. Hime¶ , M. A. Howe†† , C. Kraus‡ , R. G. H. Robertson, K. Scholbergk , M. Schumaker‡ , J. Secrest∗∗ , T. Shantz‡ , C. J. Virtue‡ , J. F. Wilkerson†† , S. Yen‡‡ , and K. Zuber§§ HALO (Helium and Lead Observatory) is under construction at SNOLAB. It will be a de- tector of supernova neutrinos with sensitivity covering most of the galaxy, but nevertheless compact, low in cost, and low in maintenance. These features are obtained through the use of Pb as a neutrino target. Neutrino interactions on Pb, both charged-current and neutral- current, populate neutron unstable states in product nuclei, and the neutrons emitted can be moderated and detected in 3 He-filled proportional counters. The counters are the ones used in the final stage of the SNO experiment to detect neutrons produced by the neutral-current interaction of solar neutrinos on deuterium. The Pb itself is also reused, originally a part of the cosmic-ray neutron detection array sited at Deep River beginning with the International Geophysical Year in 1957-58. About 76 tonnes of Pb have been preserved from that detector. The past year has seen excellent progress in the construction of HALO, beginning with the initiation of an award to the Canadian participants from NSERC (Natural Sciences and Engineering Research Council). A robust steel framework was built and the lead forms (of a special shape designed for the IGY array) installed. A water moderator and reflector surrounding the detector consists of cubical liquid container boxes that have been filled with ultrapure water. Since UW built the original NCD array (in collaboration with Los Alamos National Labo- ratory), our role has been to help with recommissioning the detectors for the new application. We have designed and built new endcaps for connecting cables individually to the 2.5-m and 3.0-m counters that will be used in HALO. The endcaps have been machined from 303 stain- less steel with the help of our new CNC lathe (see cover photograph). The endcaps accept SHV cables and contain gold-plated ball-and-socket spring-loaded connections inside (see Fig. 1.6-1). A new cutting apparatus was also built and shipped to site where it is being used to cut apart the counter “strings” that are still welded together in places. All the counters have now been moved from the storage location near the deck of the SNO cavity to a new location near HALO in the ‘ladder lab’ part of SNOLAB. We continue to work on modifying the electronics to reconfigure the readout to charge mode instead of current mode. ∗ Digipen Institute of Technology, Redmond, WA. † SNOLAB, Sudbury, ON, Canada. ‡ Laurentian University, Sudbury, ON, Canada. § University of Minnesota Duluth, Duluth, MN. ¶ Los Alamos National Laboratory, Los Alamos, NM. †† University of North Carolina, Chapel Hill, NC. k Duke University, Durham, NC. ∗∗ Armstrong Atlantic State University, Savannah, GA. ‡‡ TRIUMF, Vancouver, BC, Canada. §§ TU Dresden, Dresden, Germany.


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    30 CENTER SOCKET CONTACT CENTER SPRING BALL CONTACT Figure 1.6-1. The contacts inside the new endcaps made for the neutron detectors recycled from the third phase of SNO. SNO 1.7 Overview of the SNO experiment and CENPA’s contribution R. G. H. Robertson, R. C. Rosten, N. R. Tolich, B. VanDevender, H. S. Wan Chan Tseung, plus the SNO Collaboration. The primary scientific goal of the Sudbury Neutrino Observatory (SNO) experiment was to measure the flux of the different neutrino flavors coming from the Sun in order to understand the solar neutrino anomaly. There were three distinct phases of the experiment, each of which measured the total fluxes for all three light neutrino flavors in a different way. For the first and second phases, respectively, neutrons produced by neutrino neutral current interactions in the D2 O were observed by the gammas emitted from the subsequent neutron capture on 2 H and 35 Cl. For the third phase, proportional counters filled with 3 He were deployed within the D2 O, to detect the neutrons. Since data taking ended in November, 2006, all efforts have focussed on analysis of the recorded data. During the past year we have been working on a final analysis of the SNO data combining in a single analysis results from all three phases. This will be the most accurate result possible with the SNO data, and will likely be the most accurate solar neutrino measurement for the foreseeable future. This analysis is currently under review by a committee within the SNO collaboration before it will be distributed to the entire collaboration and published. During this analysis a number of inconsistencies in the previous analyses were investigated and resolved. The combined analysis described above is for neutrinos from the decay of 8 B within the Sun. We have also completed an internal review and are working on the publication of a search for neutrinos from the reaction 3 He + 1 H → 4 He + e+ + νe within the Sun. The


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    UW CENPA Annual Report 2010-2011 April 2011 31 standard model prediction for the flux of these neutrinos at SNO is 8.0 × 103 cm−2 s−1 . By doing an analysis including the expected neutrino energy spectrum and all the available data, this analysis reached a sensitivity at 90% confidence level of 13.0×103 cm−2 s−1 , which is more than a factor of two improvement on the previous best sensitivity, also obtained from SNO. In the past year the SNO collaboration has published a null search for neutrinos from supernova with no optical signal1 . Along with these collaboration-wide analysis efforts that have been led by Tolich; Rosten, Robertson, and VanDevender, together with a small group of other collaborators submitted for publication in Nucl. Instrum. Methods their work2 to identify two “hotspots” of back- grounds on the proportional counters. Robertson, Tolich, and Wan Chan Tseung, together with a small group of other collaborators submitted for publication in New J. Phys. their work3 developing the proportional counter simulations. The above publications complete what has been a main area of research at CENPA for more than a decade. The work has led to some very exciting results confirming that the solar neutrino anomaly was caused by neutrino oscillations. 1 B. Aharmim, et al. Astrophys. J. 728, 83 (2011) 2 CENPA Annual Report, University of Washington (2008) p. 7. 3 CENPA Annual Report, University of Washington (2008) p. 5.


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    32 2 Fundamental symmetries and non-accelerator based weak interactions Torsion balance experiments 2.1 Overview of the CENPA torsion balance experiments E. G. Adelberger A surprisingly large number of ideas for solving open problems in fundamental physics, many of which are directed at unifying gravity with the rest of physics, predict new ultra-weak forces mediated by conjectured low-mass particles. String-theory ideas are particularly prolific in this regard, as the conjectured extra dimensions and the large number of low-mass particles all produce new forces. The discovery of such forces would have a revolutionary impact, and sufficiently sensitive upper bounds on the forces severely constrain the theories. Motivated by these considerations, the CENPA Eöt-Wash group develops advanced torsion-balance techniques for sensitive mechanical measurements and applies them to address problems of current interest. We have produced the most sensitive tests of the equivalence principle1 , tested the Newtonian inverse-square law to the shortest distances2 , and have tested certain Lorentz-violating properties of electrons five orders of magnitude below the Planck scale and non-commutative geometry at the 1013 -GeV level3 . We currently operate 7 different torsion- balance instruments. Each one is devoted to a particular topic and is often the thesis project of an individual graduate student. At this moment one of the instruments is used for tests of the equivalence principle, two are used to probe short-range gravity, two to search for new electron-spin-dependent forces, and two are dedicated to investigate the subtle factors that limit the sensitivities of delicate mechanical experiments. The contributions below outline our progress in this area during the past year. This work is primarily supported by NSF grant PHY-0969199 and the salaries, etc. of faculty, students and postdocs are covered by the NSF. Costs of some equipment used in both NSF and DOE sponsored research are shared between the two funding sources. 2.1.1 Testing an equivalence principle pendulum with hydrogen-rich test bodies E. G. Adelberger, J. H. Gundlach, B. R. Heckel, S. Schlamminger∗ , W. A. Terrano Ordinary luminous matter is believed to be less than one quarter of the total mass of the universe, however these estimates rely on the assumption that the only long-range interaction between dark and luminous matter is gravity. This important assumption can be tested in ∗ National Institute of Standards and Technology, Gaithersburg, MD. 1 S. Schlamminger et al., Phys. Rev. Lett. 100, 041101 (2008). 2 D. J. Kapner et al., Phys. Rev. Lett. 78, 092006 (2008). 3 B. R. Heckel et al., Phys. Rev. D 78, 092006 (2008).


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    UW CENPA Annual Report 2010-2011 April 2011 33 the lab by looking for an equivalence-principle violating interaction between the dark matter in our galaxy and a composition dipole in our pendulum, as any non-gravitational interaction is expected to violate the equivalence principle. The sensitivity of an equivalence principle test is proportional to the degree to which the test bodies differ. To date, all equivalence- principle tests have employed test bodies that have varying degrees of neutron excess. One can gain roughly a factor of 10 in sensitivity by using test bodies of polyethylene (which has a 1 in 7 proton excess) and beryllium (which has a 1 in 9 neutron excess)1 . We are gearing up for a new version of the classic torsion balance tests of the equivalence principle with this test-body pair. The major difficulty at this point is working with a plastic material. All of our previous test bodies consisted of metals. We have built the prototype that was proposed earlier2 . This prototype will allow us to take data evaluating the thermal and mechanical stability of the ultra high molecular weight polyethylene. In order to take this data, we needed to upgrade and repair parts of the original Eöt- Wash rotating pendulum after 19 years of continuous operation. In particular the laser used to read out the twist of the pendulum was replaced with a new higher power laser that greatly increased the intensity of the angle readout signal. We also replaced the gear reducer driving the large turntable and the bearing in the co-rotating feed thru stage. 2.1.2 Progress toward improved equivalence principle limits for gravitational self-energy E. G. Adelberger, J. H. Gundlach, B. R. Heckel, S. Schlamminger∗ , and T. A. Wagner We are currently completing the analysis of our equivalence principle test using test bodies that model the difference in composition between the Earth and Moon. This experiment com- plements lunar laser ranging efforts by placing limits on the composition dependent portion of any equivalence principle violation. By combining these experimental results, a limit on equivalence principle violation due to the difference in the gravitational self-energy content of the Earth and Moon can be determined. Previously, a value of ηCD = (+0.1±2.7±1.7)×10−13 was reported by Baeßler et al.3 Due to improvements made to our apparatus over the course of this experiment, much improved noise levels were achieved in the past year. Our prelim- inary results with 1 − σ statistical uncertainty are ηCD = (7 ± 5) × 10−14 . In conjunction with improvements in lunar laser ranging4 , we expect to set a limit on η for gravitational self-energy of ∼ 10−4 . Systematic and statistical uncertainties contribute approximately equally to our lab frame results. To address two of our major systematic effects, we installed lower noise tilt sensors ∗ National Institute of Standards and Technology, Gaithersburg, MD. 1 E. G. Adelberger, J. H. Gundlach, B. R. Heckel, S. Hoedl, and S. Schlamminger, Prog. Part. Nucl. Phys. 62, 102 (2009). 2 CENPA Annual Report, University of Washington (2009) p. 31. 3 S. Baeßler, B. R. Heckel, E. G. Adelberger, J. H. Gundlach, U. Schmidt, and H. E. Swanson, Phys. Rev. Lett. 83, 3585 (1999). 4 J. G. Williams, S. G. Turyshev, and T. W. Murphy, Jr., Int. J. Mod. Phys. D, 13, 567 (2004).


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    34 (Fig. 2.1.2-1) on the apparatus this year. We began testing installation and measurement practices for these tilt sensors with a goal of obtaining a measurement of the gravity gradient field using the tilt sensors. The gravitational gradient systematic is one of our largest due to seasonal changes of the water table. Currently, we change out the pendulum for one with large gravitational moments to measure the environmental gravity gradients. If ongoing tilt sensor measurements resolve the seasonal change of the gravity gradient, we can interpolate the more sensitive pendulum measurements of the field. 100 Hz L 1 S -12 Hnrad  0.01 10-4 10-6 1 ´ 10-4 5 ´ 10-4 0.001 0.005 0.010 0.050 0.100 Frequency HHzL Figure 2.1.2-1. The noise amplitude of the existing (blue, dashed) and new, lower noise (red, solid) tilt sensors. The turntable rotation frequency is 7 × 10−4 Hz and the large peak is the 4th harmonic of the rotation frequency due to a four-fold symmetry of the apparatus support structure. 2.1.3 Submillimeter parallel plate test of gravity update J. H. Gundlach, C. A. Hagedorn, S. Schlamminger∗ , and M. D. Turner Work continues on a parallel-plate torsion balance test of the gravitational inverse square law at submillimeter scales1 . In this test, a pendulum torsion balance is used to measure the gradient of the gravitational field of an “infinite” sheet attractor at distances shorter than 100 µm. The experiment is a null-test search for violations of the inverse square law. The torsion pendulum and attractor are physically isolated by a thin metal foil held at a defined electric potential. A summer/autumn measurement campaign gave inconsistent results. Our measurements resolved a large signal (in conflict with previous experiments) that varied with time and with changes to the apparatus. We interpret the signal as being most probably caused by an unknown systematic instrumental effect. To further control possible systematic effects, we made a number of upgrades. Electrically: isolated battery-powered application of the pendulum-foil and attractor-foil voltages, battery- powered isolation amplifiers for the pendulum feedback electrodes. Pneumatic attractor drive: ∗ National Institute of Standards and Technology, Gaithersburg, MD. 1 CENPA Annual Report, University of Washington (2010) p. 35.


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    UW CENPA Annual Report 2010-2011 April 2011 35 electronic reed valve replaced with a quieter and faster fuel injector, TTL-controlled solenoid valve installed to fully shield the attractor from external pressure disturbances, and a precision absolute pressure gauge in the bellows line to allow precise determination of the attractor position without electrical connection to the apparatus. The interferometric foil monitor laser was temperature stabilized with a commercial con- troller. It is now stable enough to produce reliable measurements, but is slightly noisier than expected. An upgrade to a 660-nm fiber-coupled laser increased the intensity significantly, improving both SNR and ease-of-use. See Fig. 2.1.3-1. 1.2 foil ifo (a. u.) 1 0.8 -14 -12 -10 -8 -6 -4 -2 0 2 4 attractor-foil separation (um) Figure 2.1.3-1. Foil interferometer output as attractor presses on foil. Variable spatial frequency is due to attractor-foil misalignment. Signal variation at positive attractor-foil separation is due to interferometer drift. Improvements in data analysis include the trial implementation of bootstrapped Monte Carlo techniques for both uncertainty estimation and signal extraction. Present work includes the installation of in-vacuum motors that will allow on-line realign- ment of the foil to the attractor and repositioning of the interferometer tip. Realignment may allow a 20-micron reduction in pendulum-attractor separation. A new measurement campaign will begin in Spring 2011. 2.1.4 Progress on the wedge-pendulum probe of short-range gravity E. G. Adelberger, T. S. Cook, B. R. Heckel, and H. E. Swanson A second complete set of data has been taken with the wedge pendulum (see Fig. 2.1.4-1). Despite efforts to improve the performance of the system over the first set of data (primarily through flattening of the pendulum1 ), this set has proved to be of roughly equal quality, and did not provide the clean noise performance we hoped to obtain at close separations. As the data set was collected, it quickly became apparent that something was again wrong with the ratio of the 18-fold to 120-fold signals. The problem appeared to be in the 18-fold signal as the fit to just the 120-fold data gave very good results. Much time was spent exploring possible models to account for the discrepancy, but to no avail. The apparatus was opened to search for the causes of these problems. We believe the primary culprit for the poor noise was a piece of dust (or pieces of dust) discovered on the attractor surface and observed to be touching the electrostatic screen. 1 CENPA Annual Report, University of Washington (2010) p. 36.


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    36 Additionally, detailed scans of the outer edge of the pendulum and attractor have revealed 18-fold structure in phase with the wedges that should explain the additional amplitude in our 18-fold signal. This analysis is currently in progress. Figure 2.1.4-1. Twist data binned over 60◦ of attractor rotation showing prominent 120- fold and 18-fold signals. The data at closer separation (right) have atypically low noise for that distance; most similar runs have considerably more noise. We hope to achieve consistently less noise in the upcoming data set. Preparations are underway to attempt to collect a final set of data. The goal is to achieve reasonably clean data at attractor to pendulum separations of ≤ 60 µm. 2.1.5 Experimental limits on a proposed signature of space-time granularity from a spin polarized torsion pendulum E. G. Adelberger, B. R. Heckel, S. Schlamminger∗ , W. A. Terrano Attempts at detecting a fundamental granularity of space-time have often looked for viola- tions of Lorentz symmetry as a signal. Bonder and Sudarsky1 propose a phenomenological signature of a Lorentz invariant granularity that would manifest itself in the lab as a cou- pling between (1) the curvature of space due to the Earth and local masses, (2) the angular momentum of the Earth, and (3) the spin of the particle. We are looking for this signal using the spin-polarized pendulum2 and a large quadrupole source that can be rotated between data taking runs. Rotating the Q22 source by 90◦ changes the relative orientation of the ∗ National Institute of Standards and Technology, Gaithersburg, MD. 1 Y. Bonder and D. Sudarsky, Class. Quantum Grav. 25, 105017 (2008). 2 CENPA Annual Report, University of Washington (2003) p. 11.


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    UW CENPA Annual Report 2010-2011 April 2011 37 local curvature and the Earth’s angular momentum and shifts the lowest energy orientation of the accumulated electron spin in the pendulum. Comparing runs taken with different Q22 configurations allows us to isolate effects due to the proposed signal of Bonder and Sudarsky. In certain mass distributions used with the Q22 source we saw a non-gravitational sys- tematic effect on the pendulum. By changing the mass distributions of the sources relative to the turntable without changing the Q22 moments we found that the signal was presumably due to thermal gradients between the turntable and our Q22 source. In fact, we were able to correlate the observed twist signal with a thermal gradient across the can lid. Redesigning our Q22 source to eliminate assymetric cooling paths reduced the thermal gradient by a factor of 20. This pushes the associated systematic effect down well below our statistical uncertainty. Our results have been submitted to the Journal of Classical and Quantum Gravity. 2.1.6 Status update on a new torsion balance test of spin coupled forces E. G. Adelberger, B. R. Heckel, and W. A. Terrano The torsion balance experiment to measure spin dependent forces1 is nearly ready for commis- sioning. All that remains is assembling it in the vacuum with the torsion fiber attachments. Since our pendulum will have large numbers of aligned spins in order to be sensitive to spin coupled forces, an essential component to the experiment is demonstrating that its magnetic couplings can be controlled. To this end, after assembling the ring we tune the magnetizations of each individual segment. This reduces the measured peak to peak magnetic field 0.070 inch above the rings from 600 G to 30 G. Measurements of magnetic shielding factors on preliminary shields2 led us to a design for a set of magnetic shields which will magnetically isolate the pendulum from the attractor. These have been manufactured and annealed. We have had to redesign our system for measuring the leakage magnetic fields in order to pick up the tiny 10-ω leakage fields. This involved adding an encoder to the rotating stage so that we can average the readings from many rotations of the pendulum, and using a magneto-resistant probe instead of a hall probe for improved sensitivity. This setup should allow us to see magnetic field inhomogeneities of less than 1 µgauss. 2.1.7 Progress towards an equivalence principle test using a cryogenic torsion balance E. G. Adelberger, F. Fleischer, B. R. Heckel and H. E. Swanson As described in previous annual reports3,4 , we have built a torsion balance designed to be operated near LHe temperature. The setup will be used to investigate the limiting factors in 1 CENPA Annual Report, University of Washington (2007) p. 38. 2 CENPA Annual Report, University of Washington (2010) p. 38. 3 CENPA Annual Report, University of Washington (2009) p. 28. 4 CENPA Annual Report, University of Washington (2010) p. 40.


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    38 torsion-balance performance, and then to test the equivalence principle, using the Sun and the center of the galaxy as attractors. First tests showed excess noise significantly above the expected thermal noise level even at room temperature. This excess noise has been investigated and we have successfully identified and mitigated its sources. So far we have not yet seen an improvement in the quality factor Q of the torsion balance on cooling. There are strong hints that this may be due to eddy current damping of the pendulum motion. To overcome this limitation, a magnetic shield has been designed and is being made. Furthermore we have built a new moment-free test pendulum. Its design allows for a more sensitive and easily aligned optical readout of the twist angle. It should considerably improve the pendulum’s ability to withstand thermal cycling as well. 2.1.8 Development of an ultrasensitive interferometric quasi-autocollimator J. H. Gundlach, C. A. Hagedorn, S. Schlamminger∗ , and M. D. Turner We have developed an angular deflection measurement device called the interferometric quasi- autocollimator (iQuAC). This has potential use in any of our group’s torsion balance exper- iments. It uses the quantum weak value amplification effect1 and is based on the setup described by Dixon et al.2 −8 10 −9 ← calibration signal 10 Angle noise (rad/rt−Hz) −10 acoustic sources 10 −11 10 −12 10 0 1 2 10 10 10 Frequency (Hz) (a) (b) Figure 2.1.8-1. (a) A schematic diagram of the iQuAC device. (b) The noise floor of an implementation of the iQuAC design. A 620-prad calibration signal at 2 Hz is used to calibrate the device. Our torsion balances are monitored by autocollimators that our group has designed and constructed. The best of these autocollimators has a sensitivity of ∼ 1 nm. Although the amplification scheme used by Dixon et al. can measure much smaller angles, it is sensitive ∗ National Institute of Standards and Technology, Gaithersburg, MD. 1 Y. Aharonov, D.Z. Albert, and L. Vaidman, Phys. Rev. Lett. 60, 1351 (1988). 2 P. B. Dixon, D. J. Starling, A. N. Jordan, and J. C. Howell, Phys. Rev. Lett. 102, 173601 (2009).

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