Majorana Neutrinoless Double-Beta Decay Experiment

1
Majorana Neutrinoless Double-Beta Decay Experiment
Brown University, Providence, Rhode
Island Institute for Theoretical and Experimental
Physics, Moscow, Russia Joint Institute for
Nuclear Research, Dubna, Russia Lawrence Berkeley
National Laboratory, Berkeley, California Lawrence
Livermore National Laboratory, Livermore,
California Los Alamos National Laboratory, Los
Alamos, New Mexico Oak Ridge National Laboratory,
Oak Ridge, Tennessee Osaka University, Osaka,
Japan
Pacific Northwest National Laboratory, Richland,
Washington Queen's University, Kingston,
Ontario Triangle Universities Nuclear Laboratory,
Durham, North Carolina and Physics Departments at
Duke University and North Carolina State
University University of Chicago, Chicago,
Illinois University of South Carolina, Columbia,
South Carolina University of Tennessee,
Knoxville, Tennessee University of Washington,
Seattle, Washington

• GERDA Collaboration Meeting
• June 28, 2005
• Dubna, Russia

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The Majorana 76Ge 0nbb-Decay Experiment

• Based on Ge crystals
• 180 kg 86 76Ge
• Enriched via centrifugation
• Modules with 57 crystals each
• Three modules for 180 kg
• Eight modules for 500 kg!
• Maximal use of copper electroformed underground
• Background rejection methods
• Granularity
• Pulse Shape Discrimination
• Single Site Time Correlation
• Detector Segmentation
• Underground Lab
• 6000 mwe
• Class 1000

3
Conceptual Design of 57 Crystal Module

• Conventional vacuum cryostat made with
  electroformed Cu
• Three-crystal tower is a module within a module
• Allows simplified detector installation
  maintenance
• Low mass of Cu and other structural materials per
  kg Ge

40 cm x 40 cm Cryostat
Cap
Tube (0.007 wall thickness)
Ge (62mm x 70 mm)
Tray (Plastic, Si, etc)
4
Shield Design

• Allows modular deployment, early results
• 40 cm bulk Pb, 10 cm ULB shielding
• 4p veto shield
• Sliding 5 ton doors (prototype under ME test)

5
Background Goals and Demonstrated Levels

• Simulation connects activity to expected count
  rate
• Background target 1 count/ROI/ton-year
• Three years run time with this level (0.5
  ton-year) 5 x 1026 y

Bkg Location Purity Issue Activation Rate Target Exposure Ref.
Ge Crystals 68Ge 60Co 1 atom/kg/day 100 d Avi92
Target Mass Target Purity Achieved Assay
Inner Mount 232Th 2 kg 1 mBq/kg 2-4 mBq/kg Arp02 more recent work
Cryostat 232Th 38 kg 1 mBq/kg 2-4 mBq/kg Arp02 more recent work
Cu Shield 232Th 310 kg 1 mBq/kg 2-4 mBq/kg Arp02 more recent work
Small Parts 232Th 1 g/crystal 1 mBq/kg 1 mBq/kg Mil92
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Ge Exposure Timeline

• Conservative estimate of 100 days exposure taken
• Doubling this or spallation rate (1 atom/kg/day _at_
  surface) adds only 3 to total rate

Process Step Minimum Estimated Time Effective Time (with shield)
Enrichment (ECP Zelenogorsk) 90 days 1 day
Shipping Zelenogorsk to Oak Ridge 32 days 3.2 days
Production of metal and initial refinement 11 days 11 days
Manufacturers zone refinement 14 days 14 days
Crystal growth 4 days 4 days
Mechanical preparation 3 days 3 days
Detector Fabrication 7 days 7 days
Total 161 days 44.2 days
Shipping Concept 2m cube
Storage Concept 4m cube
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Granularitydetector-to-detector rejection
40 cm

• Simultaneous signals in two detectors cannot be
  0nbb
• Requires tightly packed Ge
• Successful against
• 208Tl and 214Bi
• Supports/small parts (5x)
• Cryostat/shield (2x)
• Some neutrons
• Muons (10x)
• Simulation and validation with Clover

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Pulse Shape Discrimination
Central contact (radial) PSD

• Excellent rejection for internal 68Ge and 60Co
  (x4)
• Moderate rejection of external 2615 keV (x0.8)
• Shown to work well with segmentation
• Demonstrated capability
• Central contact
• External contacts
• Requires 25 MHz BW

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Time Correlations

• 68Ge is worst initial raw background
• 68Ge -gt 10.367 keV x-ray, 95 eff
• 68Ga -gt 2.9 MeV beta
• Cut for 3-5 half-lives after signals in the 11
  keV X-ray window reduces 68Ga b spectrum
  substantially
• Independent of other cuts

QEC 2921.1
3 , 5 t1/2 cut
No cut
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Crystal Segmentation

• Segmentation
• Multiple conductive contacts
• Additional electronics and small parts
• Rejection greater for more segments
• Background mitigation
• Multi-site energy deposition
• Simple two-segment rejection
• Sophisticated multi-segment signal processing
• Demonstrated with
• GEANT4 (MaGe) calculations
• MSU experiment

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Segmentation Study Experiment and Simulation

• 60Co on the side of the detector
• Simple multiplicity cuts No PSD

Experiment
Crystal
Counts / keV / 106 decays
Crystal
GEANT
1x8
1x8
4x8
4x8
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Ultra-Pure Electroformed Cu

• Th chain purity is key
• Ra and Th must be eliminated
• Successful Ra ion exchange C
• Th ion exchange under development
• Demonstrated gt8000 Th rejection via
  electroplating from A-gtB
• Starting stock A lt9 mBq/kg 232Th
• Intensive development of assay to achieve 1
  mBq/kg 232Th of A, B, and C, and, possibly much
  less
• Based on ICPMS of nitric etch soln
• Would allow QA of each part

30 cm x 30 cm Cryostat
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Small Parts Low-background Front-end Electronics
Package LFEP
ORTEC
LFEP3 (IGEX)
LFEP4
Material Mass (grams)
Circuit Board (PTFE, Cu, Au) 0.32974
JFET 1.5E-4
RhO2 Resistor 5.9E-4
Al wirebond wire 2E-5
Silver-Loaded Epoxy 1E-4
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Design DriversAnalog Performance Needed for PSD

• Commercial digital spectroscopy hardware used for
  current PNNL PSD has 40 MHz, 14-bit digitization
• Sampling rate is good match with
  easily-achievable HPGe preamp bandwidth

Full-energy 1621-keV g (top) and 1592-keV DEP
(bottom) reconstructed current pulses from 120
P-type Ortec HPGe detector (experimental data)
Response of Ortec HPGe 237P preamplifier
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Multi-Parametric Pulse-Shape Discriminator

• Extracts key parameters from each preamplifier
  output pulse
• Sensitive to radial location of interactions and
  interaction multiplicity
• Self-calibrating allows optimal discrimination
  for each detector
• Discriminator can be recalibrated for changing
  bias voltage or other variables
• Method is computationally cheap, requiring no
  computed libraries-of-pulses

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An old demonstrated result with 12 bit 40 MHz
digitization rate
Keeps 80 of the single-site DEP (double escape
peak)
Experimental Data
Rejects 74 of the multi-site backgrounds (use
212Bi peak as conservative indicator)
Original spectrum
Scaled PSD result
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Previous Front-End Results
Rise-times for various experimental
configurations. The pulser rise-time for these
tests was 15 ns.

• All tests used PGT RG-11 as preamp back-end

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Disasters Do Happen
Punishment for yielding 120 ns 10 - 90
performance

• We didnt really like that FET anyway

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Current LFEP Module Performance(2N4356 FET
w/92cm leads)
40 ns 10-90
output pulse
input power
output power
input pulse
25 MHz
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Background Goals
Dominated by 232Th in Cu
At this level, we might not get a count in a 3
year run!
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Cuts vs. Background Estimates
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Construction vs. Operations
68Ge build up and decay
Ops Begins
80 of total 68Ge has decayed
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Majorana Sensitivity vs. Time

• 180 kg 86 76Ge operated for 3 years
• 0.46 t-y of 76Ge or 0.54 t-y total Ge

Effect of background
0 cts/ROI/ty Ideal
1 cts/ROI/ty target
8 cts/ROI/ty certain (IGEX levels with new data
cuts applied)
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A Recent Claim
Klapdor-Kleingrothaus H V, Krivosheina I V, Dietz
A and Chkvorets O, Phys. Lett. B 586 198 (2004).
Used five 76Ge crystals, with a total of 10.96 kg
of mass, and 71 kg-years of data. ?1/2 1.2 x
1025 y 0.24 lt mv lt 0.58 eV (3 sigma)
Background level depends on intensity fit to
other peaks.
Expected signal in Majorana (for 0.456 t-y) 135
counts With a background Goal lt
1 cnt in the ROI (Demonstrated lt 8 cnts in the
ROI)
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Reference Schedule
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Majorana Sensitivity Realistic runtime
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GERDA Relationship

• GERDA Collaboration using 20 kg of existing
  (IGEXHM) 76Ge crystals (Phase 1) and 35kg new
  Ge (Phase 2) to achieve sensitivity past KKDC
• New approach for Phase 1 2
• Ge immersed in cryogen in large tank in LNGS
• Signed MOU to cooperate in early years and merge
  for unified ultimate thrust, using most effective
  technologies and concepts
• Continued careful cooperation and coordination
  very important!

GERDA P1 20 kg
GERDA P2 35 kg
Joint experiment 1000 kg
Majorana 180 kg
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Majorana Summary

• As in Gerda, backgrounds are key
• We have begun proposing a modular plan for
  intermediate (180 kg) scale with potential for
  expansion to ton scale
• The NuSAG Committee is expected to recommend a
  double-beta decay research plan by mid to late
  July

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The Majorana Collaboration
Brown University, Providence, Rhode
Island Michael Attisha, Rick Gaitskell, John-Paul
Thompson Institute for Theoretical and
Experimental Physics, Moscow, Russia Alexander
Barabash, Sergey Konovalov, Igor Vanushin,
Vladimir Yumatov Joint Institute for Nuclear
Research, Dubna, Russia Viktor Brudanin, Slava
Egorov, K. Gusey, S. Katulina, Oleg Kochetov, M.
Shirchenko, Yu. Shitov, V. Timkin, T. Vvlov, E.
Yakushev, Yu. Yurkowski Lawrence Berkeley
National Laboratory, Berkeley, California Yuen-Dat
Chan, Mario Cromaz, Martina Descovich, Paul
Fallon, Brian Fujikawa, Bill Goward, Reyco
Henning, Donna Hurley, Kevin Lesko, Paul Luke,
Augusto O. Macchiavelli, Akbar Mokhtarani, Alan
Poon, Gersende Prior, Al Smith, Craig
Tull Lawrence Livermore National Laboratory,
Livermore, California Dave Campbell, Kai
Vetter Los Alamos National Laboratory, Los
Alamos, New Mexico Mark Boulay, Steven Elliott,
Gerry Garvey, Victor M. Gehman, Andrew Green,
Andrew Hime, Bill Louis, Gordon McGregor,
Dongming Mei, Geoffrey Mills, Larry Rodriguez,
Richard Schirato, Richard Van de Water, Hywel
White, Jan Wouters Oak Ridge National
Laboratory, Oak Ridge, Tennessee Cyrus Baktash,
Jim Beene, Fred Bertrand, Thomas V. Cianciolo,
David Radford, Krzysztof Rykaczewski
Osaka University, Osaka, Japan Hiroyasu Ejiri,
Ryuta Hazama, Masaharu Nomachi Pacific Northwest
National Laboratory, Richland, Washington Craig
Aalseth, Dale Anderson, Richard Arthur, Ronald
Brodzinski, Glen Dunham, James Ely, Tom Farmer,
Eric Hoppe, David Jordan, Jeremy Kephart, Richard
T. Kouzes, Harry Miley, John Orrell, Jim Reeves,
Robert Runkle, Bob Schenter, Ray Warner, Glen
Warren Queen's University, Kingston,
Ontario Marie Di Marco, Aksel Hallin, Art
McDonald Triangle Universities Nuclear
Laboratory, Durham, North Carolina and Physics
Departments at Duke University and North Carolina
State University Henning Back, James Esterline,
Mary Kidd, Werner Tornow, Albert
Young University of Chicago, Chicago,
Illinois Juan Collar University of South
Carolina, Columbia, South Carolina Frank
Avignone, Richard Creswick, Horatio A. Farach,
Todd Hossbach, George King University of
Tennessee, Knoxville, Tennessee William Bugg,
Yuri Efremenko University of Washington,
Seattle, Washington John Amsbaugh, Tom Burritt,
Jason Detwiler, Peter J. Doe, Joe Formaggio, Mark
Howe, Rob Johnson, Kareem Kazkaz, Michael Marino,
Sean McGee, Dejan Nilic, R. G. Hamish Robertson,
Alexis Schubert, John F. Wilkerson