The Majorana Project: A Next-Generation Double Beta Decay Experiment

1. The Majorana Project:A Next-Generation Double Beta Decay Experiment Victor M. Gehman For the Majorana Collaboration LA-UR-05-8062 • Physics Motivation • Why 76Ge? • Majorana Overview • Sensitivity/Background Goals • Readiness and Recent R&D • Conclusions

2. e- _  Z, A _  Z+1, A e- e- Z, A _ Z+2, A  , Z+1, A e- Z+2, A U. Zargosa Physics Motivation:  decay? • Most “even-even” nuclei are stable against  decay • For some there’s a rare Z = ±2 transition • 2: Allowed in the standard model • Essentially two simultaneous  decays • : Requires the  be reabsorbed by intermediate nucleus • This reabsorption requires that: •  is its own antiparticle •  is not in a pure helicity state (must have a nonzero mass) • Lepton number conservation is violated

3. Physics Motivation: Neutrinos • We’re all (well, getting to be) on the same page now! • We know the minimum neutrino mass scale from mass differences measured in oscillations experiments • The next step is an experiment sensitive to neutrino mass scales of ≈100 of meV • Also get consistent limits from cosmology • A new 0 with a 10-100 fold increase in sensitivity can explore this mass range • Such an experiment would probe fundamental physics: • Are neutrinos their own antiparticles (Majorana)? • What is the absolute mass scale of the neutrino? • Is lepton number symmetry violated?

4. U. Zargosa Why 76Ge? Ge diodes are intrinsically clean! Very few non-active materials in the array! Just 4 keV at 2039 keV! Demonstrated ability to enrich 76Ge from 7.44% (natural) to 86%. Can build large arrays of closely packed detectors. 0 (if it exists) will be an EXTREMLEY rare decay! To observe it, we would need: • Large source mass • Highly efficient detector • VERY low (nearly zero) background in 0 ROI • Ultra-clean materials and sophisticated event tagging techniques • Best possible energy resolution • Allows for a narrower ROI • Helps separate 2 from 0 Keeps 2 Continuum from bleeding into 0 peak e- have a range of ≈ 1mm in Ge metal. Since the source IS the detector, very few  events will be missed! Pulse shape analysis and detector segmentation are powerful methods for event classification

5. Veto Shield Sliding Monolith LN Dewar Inner Shield 57 Detector Module Majorana Project Overview… • Majorana is intended to be a scalable experiment • Array contains up to eight 57-detector modules on four independently sliding monoliths • Shielding: 4 active veto, 40cm bulk lead, 10cm ultra-low background inner shield

6. Vacuum jacket Cap Cold Plate Tube (0.007” wall) Cold Finger Ge (62mm x 70 mm) 1.1 kg Crystal Tray (Plastic, Si, etc) Thermal Shroud Bottom Closure Majorana Detector Modules… • The plan is to put 57 roughly 1 kg detectors in each module • Conventional vacuum cryostat made from electroformed copper • Each three-crystal stack is individually removable

7. <m> of 100 meV nucl-th/0503063 Sensitivity and Background… • <m> sensitivity of 100 meV  T1/2 sensitivity of a few1026 y • Our sensitivity is ultimately limited by signal to background ratio • This means our background has to be ≈ 1 count / tonne-year

8. Background Reduction: Two Strategies… • While building the experiment: • Select ultra-pure materials • Minimize “non-source” material • Clean passive shielding • Go deep to reduce  and related activity • While collecting and analyzing the data: • Active veto • Excellent energy resolution • Single-site vs. multi-site event discrimination •  events are single-site • Most of our backgrounds will be multi-site events • Use granularity, pulse shape analysis and detector segmentation •  events are also single-site in time, whereas many of our backgrounds are part of a decay chain

9. Readiness and R&D… • Simulations: MaGe framework • Based on Geant4 and being developed in cooperation with the Gerda collaboration • Verified against a variety of detectors • Also use Fluka for -induced backgrounds, tested against underground lab data • Assay (Goal: 1 Bq/kg (0.25 pg/g) for 232Th in Cu) • Radiometric: ≈ 8 Bq/kg (2 pg/g) • Counting facilities at PNNL, Oroville (LBNL), WIPP (LANL), Soudan, and Sudbury • Mass Spectroscopy: • Using “Inductively Coupled Mass Spectroscopy” (ICPMS) • Currently limited by reagent cleanliness - being addressed! • Technique should have requisite sensitivity

10. 208Tl DEP 228Ac  Readiness and R&D… • PSA and Segmentation: • Demonstrated the efficacy with the LANL Clover detector (nucl-ex/0509026) and 5x8 detector at MSU • Array Granularity: • Requires tightly-packed array • Successful against: • 208Tl and 214Bi (support structure/small parts at 5x and cryostat/shield at 2x) • Some neutrons • Muons at 10x • Simulation and validation with clover

11. Conclusions… • The Majorana project satisfies the APS multi-divisional goals for probing the quasi-degenerate  mass scale • Majorana is scalable to 500 - 1000 kg • Majorana improves upon the previous generation of 0 experiments: • An order of magnitude more 76Ge • About two orders of magnitude lower background • Improved design and detector technology should yield ≈ 30 x better background rejection • We are confident we can reach a lifetime limit of 5.5 x 1026 y (90% CL) or a  mass of 100 meV, or perform a 10% measurement at the KKDC claim • We have built a large, experienced collaboration with the skills necessary to design, construct and operate this experiment!

12. 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, OlegKochetov, 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 • 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, Fraser Duncan, 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 Note: Red text indicates students