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The Majorana Project: A NextGeneration Neutrino Mass Probe

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The Majorana Project: A Next-Generation ... Los Alamos National Laboratory, Los Alamos, NM. Steve Elliott, Andrew Hime ... Harry Miley, Co-spokesperson ... – PowerPoint PPT presentation

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Title: The Majorana Project: A NextGeneration Neutrino Mass Probe


1
The Majorana Project A Next-Generation Neutrino
Mass Probe
  • Craig AalsethforThe Majorana Collaboration
  • NDM03, Nara, Japan
  • June 9, 2003

2
The Majorana Collaboration
Brown University, Providence, RI Rick Gaitskell
Duke University, Durham, NC Werner
Tornow Institute for Theoretical and
Experimental Physics, Moscow, RussiaA. Barabash,
S. Konovalov, V. Stekhanov, V. Umatov Joint
Institute for Nuclear Research, Dubna, RussiaV.
Brudanin, S. Egorov, O. Kochetov, V. Sandukovsky
Lawrence Berkley National Laboratory, Berkley,
CAPaul Fallon, I. Y. Lee Lawrence Livermore
National Laboratory, Livermore, CAKai Vetter
Los Alamos National Laboratory, Los Alamos,
NMSteve Elliott, Andrew Hime New Mexico State
University, Carlsbad, NMJoel Webb
North Carolina State University, Raleigh, NC Eric
Adles, Rakesh Kumar Jain, Jeremy Kephart, Ryan
Rohm, Albert Young Osaka University, Osaka,
Japan Hiro Ejiri, Ryuta Hazama, Masaharu Nomachi
Pacific Northwest National Laboratory,
Richland, WAHarry Miley, Co-spokesperson Craig
Aalseth, Dale Anderson, Ronald Brodzinski,
Shelece Easterday, Todd Hossbach, David Jordan,
Richard Kouzes, William Pitts, Ray Warner
University of Chicago, Chicago, ILJuan Collar,
University of South Carolina, Columbia, SCFrank
Avignone, Co-spokesperson Horacio Farach,
George King, John M. Palms, University of
Washington, Seattle, WA Peter Doe, Victor Gehman,
Kareem Kazkaz, Hamish Robertson, John Wilkerson
  • http//majorana.pnl.gov

3
Outline
  • Introduction and Overview
  • Reference Concept
  • Backgrounds and Mitigation
  • Pulse-Shape Discrimination
  • Detector Segmentation
  • Experiment Sensitivity
  • Progress and Status
  • Conclusions

4
Germanium Basics
  • Internal Source Method from Fiorini
  • 76Ge Endpoint 2039 keV
  • Energy above many contaminants
  • Except 208Tl, 60Co, 68Ge
  • FWHM 3-4 keV around 2 MeV (0.2)
  • Long experience with Ge bb decay
  • Previous efforts found 2n at T1/2 1021 y
  • Expect 0n at T1/2 4 x 1027 y
  • Ready to go!
  • Essentially no RD needed

5
Majorana Overview
  • GOAL Sensitive to effective Majorana n mass as
    low as 0.02-0.07 eV
  • 0n bb-decay of 76Ge potentially measured at 2039
    keV
  • Based on well known 76Ge detector technology
    plus
  • Pulse-shape analysis
  • Detector segmentation
  • Ready to begin now
  • Requires
  • Deep underground location
  • 500 kg enriched 85 76Ge
  • Many crystals, each segmented
  • Advanced signal processing
  • Pulse shape discrimination
  • Special low background materials
  • Reference Configuration

6
Majorana Reference Concept
3-D model of reference configuration
  • Optimization underway of performance and risk
  • Several low-risk designs possible
  • Many segmentation schemes possible
  • Alternative packaging, cooling, shielding under
    consideration
  • Nature of Ge crystals allows repackaging

7
Starting Background Estimate
  • International Germanium Experiment (IGEX)
    achieved between 0.1-0.3 counts/keV/kg/y
  • Documented experiences with cosmic secondary
    neutron production of isotopes

Calculated Experimental
Bro95 R. L. Brodzinski, et al, Journal of
Radioanalytical and Nuclear Chemistry, Articles,
Vol. 193, No. 1 (1995) 61-70.
8
Single-site interaction example
Monte-Carlo 2038-keV deposition from 0n bb-decay
of 76Ge
9
Multiple-site interaction example
Monte-Carlo 2038-keV deposition from
multi-Compton of 2615-keV 208Tl g
10
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

11
PSD can reject multiple-site backgrounds (like
68Ge and 60Co)
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
Improves T1/2 limit by 56
12
Detector Segmentation
  • Sensitive to axial and azimuthal separation of
    depositions
  • reference design with six azimuthal and two axial
    contacts is low risk
  • This level of segmentation gives good background
    rejection
  • This segmentation gives us 2500 segments of 200
    g or 40 cc

13
Monte-Carlo Example(single crystal)
Segment multiplicity at 2039 keV
Sensitive to z and phi separation of depositions
0nbb efficiency 91 internal 60Co efficiency
14 Improves T1/2 limit by 140
  • Next Steps
  • T ½ improvement increases to 260 - 620 when
    including array self-shielding, depending on
    position of crystal not included in earlier
    background estimate
  • Time-series analysis of background very promising

14
Sensitivity vs. Time
  • Slow Production Gradual ramp to 100 kg/y - total
    500 kg 85 76Ge
  • Fast Production 200 kg/y (No
    ramp)
  • Present 0nbb 76Ge T1/2 limit rapidly surpassed
    (T1/2 gt 1.9 1025 y)

0nbb Half-Life
  • Based on early IGEX background levels with
    reasonable background reduction and cutting
    methods applied

15
Examples of signal intensity
T1/2 1.5 1025y 95 counts 50 kg-y
  • T1/2 1 1026y
  • 28 counts
  • 1000 kg-y

16
Collaboration ProgressOptimizations for Full
Experiment
Multi Element Germanium Assay (MEGA) 162
natural Ge
MAJORANA 500 kg Ge detectors All
enriched/segmented Multi-crystal modules
g
Segmented Enriched Germanium Array
(SEGA) Segmented Ge
1 to 5 Crystals First enriched, segmented
detector in testing! Additional tests being
planned for other segmented systems
High density Materials qualification Cryogenic
design test Geometry signal routing
test Powerful screening tool
Full Experiment
17
Progress and StatusSEGA Segmentation
Optimization
  • First (enriched) 6x2 SEGA operating
  • Current Testing (TUNL)
  • Shallow UG testing at U Chicago LASR facility
  • Operation in WIPP
  • Second and third SEGA planning
  • Funds in hand (LANL, USC)
  • Alternate segmentation testing in planning
    (USC/PNNL)
  • 40-fold-segmented LLNL detector now available

SEGA crystal initial test cryostat
Figure-Of-Merit vs. Axial Azimuthal
Segmentationfor internal 60Co background
18
Progress and StatusMEGA Cryogenic testing
  • Materials in hand
  • Detectors (20 - 70 HPGe), electronics
  • Assembly and cryogenic testing of two-packs
    underway (PNNL, UW, NC State)
  • UG facility (WIPP) in prep (LANL, NMSU)
  • Summer installation anticipated
  • Sensitive to 1e4 short-lived atoms

19
Recent Crystal Packaging Test(MEGA)
20
Progress and StatusUltra-Low Level Screening
  • Screening facility
  • Operating in Soudan (Brown U)
  • Some contamination issues 207Bi
  • Two HPGE detectors (1.05 kg, 0.7 kg)
  • Planned use for screening
  • Minor materials used in manufacturing
  • Improved Cu testing
  • Small parts qualification
  • FET, cable, interconnects, etc

Dual counter shield 1.05 and 0.7 kg detectors
21
Progress and StatusLow-Background Electroformed
Copper
  • Can be easily formed into thin, low-mass parts
  • Recent designs reduce MCu/MGe x5
  • UG Electroforming can reduce cosmogenics
  • Pre-processing can reduce U-Th
  • Recent results suggest cleaner than thought

Electroformed cups shown have wall thickness of
only 250 mm!
22
Conclusions
  • Unprecedented confluence
  • Enrichment availability/Neutrino mass interest/
    Underground facility development
  • High Density
  • Modest apparatus footprint, no special lab
    required
  • Low Risk
  • Proven technology/ Modular instrument /
    Relocatable
  • Experienced and Growing Collaboration
  • long bb track record, many technical resources
  • Neutrino mass sensitivity
  • potential for discovery

23
Thank You NDM03, Nara
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