Victor M. Gehman

1
The Majorana ProjectA 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 RD
• Conclusions

2
Physics Motivation ?? decay?

• Most even-even nuclei are stable against ?
  decay
  
• For some theres 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

• Were 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
Why 76Ge?

• 0??? (if it exists) will be an EXTREMELY rare
  decay!
  
• To observe it, we would need
• Large source mass - Demonstrated enrichment
  technology and ability to construct large arrays
  
• Highly efficient detector - Short range of e- in
  Ge combined with active source technique means
  we will miss very few ?? events
  
• VERY low (nearly zero) background in 0??? ROI
• Ultra-clean materials - Ge diodes are
  intrinsically clean, otherwise they couldnt work
  as detectors
  
• Sophisticated event tagging techniques - powerful
  event classification capability from PSA and
  detector segmentation
  
• Best possible energy resolution
• Allows for a narrower ROI - just 4 keV at 2039
  keV!
  
• Helps separate 2??? from 0??? - keeps 2???
  continuum from bleeding into 0??? peak

5
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
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
Majorana Reference Plan

• Enrichment Ge 200 kg of intrinsic Ge metal,
  enriched to 86 in 76Ge, from the ECP in Russia
  
• Transport surface ship Ge to manufacturing
  company in North America to produce crystals, for
  detector fabrication
  
• Crystals produce 180 1.1-kg, n-type, segmented
  Ge detectors each with 2 segments
  
• Module Assembly install detectors into Cu
  cryostats that were electroformed underground
  
• Module Installation install modules into an
  ultra-pure graded shield
  
• Shielding incorporate an active, neutron and
  cosmic ray anti-coincidence detector (a veto
  system) into the Pb shield, deep underground
  
• Front End Signals read out the Ge detectors with
  one high-bandwidth channel per crystal and one
  low-bandwidth channel per segment
  
• Acquisition use commercial electronics for the
  data acquisition

8
Sensitivity and Background

• 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

9
A Recent Claim
Klapdor-Kleingrothaus H V, Krivosheina I V, Dietz
A and Chkvorets O, Phys. Lett. B 586 198 (2004).
KKDC 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 (3 sigma)
10
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

11
Cuts vs. Background Estimates
The fact that our signal is a peak at 2039 keV
combined with our cuts discriminates 0??? from
backgrounds
12
Readiness and RD

• 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

13
Readiness and RD

• 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

14
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!

15
The Majorana Collaboration
Brown University, Providence, Rhode Island
Michael Attisha, Rick Gaitskell, John-Paul
Thompson Institute for Theoretical and Experime
ntal Physics, Moscow, Russia Alexander Barabash,
Sergey Konovalov, Igor Vanushin, Vladimir
Yumatov Joint Institute for Nuclear Research, D
ubna, Russia Viktor Brudanin, Slava Egorov, K. Gu
sey, 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 Croma
z, 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, Livermor
e, California Dave Campbell, Kai Vetter Los Al
amos 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, Tennes
see Cyrus Baktash, Jim Beene, Fred Bertrand, Thom
as 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, Kin
gston, Ontario Marie Di Marco, Fraser Duncan, Aks
el Hallin, Art McDonald Triangle Universities N
uclear Laboratory, Durham, North Carolina and
Physics Departments at Duke University and North
Carolina State University Henning Back, James Est
erline, Mary Kidd, Werner Tornow, Albert Young
University of Chicago, Chicago, Illinois Juan C
ollar University of South Carolina, Columbia, S
outh Carolina Frank Avignone, Richard Creswick, H
oratio A. Farach, Todd Hossbach, George King
University of Tennessee, Knoxville, Tennessee W
illiam Bugg, Yuri Efremenko University of Washi
ngton, Seattle, Washington John Amsbaugh, Tom Bur
ritt, 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