Transcript The Majorana Project: A Next- Generation Neutrino Mass Probe The Majorana Collaboration

The Majorana Project: A NextGeneration Neutrino Mass Probe
Craig Aalseth
for
The Majorana Collaboration
NDM03, Nara, Japan
June 9, 2003
The Majorana Collaboration
Brown University, Providence, RI
Rick Gaitskell
Duke University, Durham, NC
Werner Tornow
Institute for Theoretical
and Experimental Physics, Moscow, Russia
A. Barabash, S. Konovalov, V. Stekhanov, V. Umatov
Joint Institute for
Nuclear Research, Dubna, Russia
V. Brudanin, S. Egorov, O. Kochetov, V. Sandukovsky
Lawrence Berkley
National Laboratory, Berkley, CA
Paul Fallon, I. Y. Lee
Lawrence Livermore
National Laboratory, Livermore, CA
Kai Vetter
Los Alamos National Laboratory, Los Alamos, NM
Steve Elliott, Andrew Hime
New Mexico State University, Carlsbad, NM
Joel 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, WA
Harry 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, IL
Juan Collar,
University of South Carolina, Columbia, SC
Frank 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
Outline
Introduction and Overview
Reference Concept
Backgrounds and Mitigation
– Pulse-Shape Discrimination
– Detector Segmentation
Experiment Sensitivity
Progress and Status
Conclusions
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 R&D needed
Majorana Overview
ep+
p+
e-
n
ne
n
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
Reference Configuration
– Special low background materials
Majorana Reference Concept
3-D model of reference configuration
210 2.35 kg crystals
Segmentation (6x2) results in
2500 individual 200g segments
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
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
Spallation
Isotope
68
Ge
56
Co
60
Co
58
Co
Total
T1/2 (d)
270.82
77.27
1925.2
70.82
Rate from
After
[Bro95]
Construction
0.1562
0.03702
0.0238
0.00212
0.0177
0.01294
0.0024
0.000202
cts/keV/kg/y cts/keV/kg/y
0.2
0.0523
Calculated
Experimental
Rate During
Experiment
3.93E-03
6.43E-05
7.15E-03
5.60E-06
cts/keV/kg/y
0.0112
Total in
ROI
70.15
1.15
127.55
0.10
Counts
198.95
After PSD
Rejection
18.59
0.30
33.80
0.03
Counts
52.72
After Seg
Rejection
2.57
0.04
4.66
0.00
Counts
7.28
[Bro95] R. L. Brodzinski, et al, Journal of Radioanalytical and Nuclear Chemistry, Articles, Vol. 193, No. 1 (1995) 61-70.
Single-site interaction example
Monte-Carlo 2038-keV deposition
from 0n bb-decay of 76Ge
Multiple-site interaction example
Monte-Carlo 2038-keV deposition
from multi-Compton of 2615-keV 208Tl g
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
PSD can reject multiple-site backgrounds
(like 68Ge and 60Co)
212Bi
DEP of
208Tl
1592.5 keV
1620.6 keV
Experimental Data
228Ac
1587.9 keV
Original
spectrum
Scaled
PSD result
Keeps 80% of the
single-site DEP
(double escape
peak)
Rejects 74% of the
multi-site
backgrounds
(use 212Bi peak as
conservative indicator)
Improves T1/2
limit by 56%
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
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 selfshielding, depending on
position of crystal – not
included in earlier
background estimate
• Time-series analysis of
background very promising
Sensitivity vs. Time
1.E+28
Fast Production
27
4.0 10  <mn> = [0.02 - 0.07] eV
2.0 1027  <mn> = [0.03 - 0.10] eV
Slow Production
1.E+27
1.0 1027  <mn> = [0.04 - 0.14] eV
0nbb Half-Life
Slow Production:
Gradual ramp to
100 kg/y - total
500 kg 85% 76Ge
Fast Production:
200 kg/y
(No ramp)
Present 0nbb
76Ge T
1/2 limit
rapidly
surpassed
(T1/2 > 1.9 1025 y)
26
2.5 10  <mn> = [0.08 - 0.28] eV
1.E+26
Today's Best Limit
1.E+25
0
2
4
6
8
10
Time (Years)
Based on early IGEX background levels with reasonable
background reduction and cutting methods applied
12
Collaboration Progress:
Optimizations for Full Experiment
Multi
Element
Germanium
Assay
(MEGA):
16+2
natural Ge
MAJORANA:
500 kg Ge detectors
All enriched/segmented
g
Multi-crystal modules
Segmented
Enriched
Germanium Array
(SEGA):
Segmented Ge
1 to 5 Crystals
First enriched, segmented
detector in testing!
High density
Additional tests being planned
for other segmented systems
Cryogenic design test
Materials qualification
Geometry & signal routing test
Powerful screening tool
Full Experiment
Progress and Status
SEGA: 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 Segmentation
for internal 60Co background
Progress and Status
MEGA: 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
Recent Crystal Packaging Test
(MEGA)
Progress and Status
Ultra-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
Dual counter shield: 1.05 and 0.7 kg detectors
• FET, cable, interconnects, etc
Progress and Status
Low-Background Electroformed Copper
Electroformed cups shown have wall
thickness of only 250 mm!
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
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
Thank You
NDM03, Nara