Double Beta Decay

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Double Beta Decay Cuore Majorana Dingb
at
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Only way to distinguish Dirac vs. Majorana, and
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(NRC report, NESS)
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CUORE
Cryogenic Underground Laboratory for Rare Events
J. W. Beeman1, E. E. Haller1,2, R.J. McDonald1,
E. B. Norman1, A. R. Smith1, A. Giuliani3 , M.
Pedretti3, G. Ventura4, M. Balata5, C. Bucci5, C.
Pobes5, V. Palmieri6, G. Frossati7, A. de
Waard7, C. Brofferio8, S. Capelli8, L. Carbone8,
O. Cremonesi8, E. Fiorini8, D. Giugni8, P.
Negri8, A. Nucciotti8, M. Pavan8, G. Pessina8,
S. Pirro8, E. Previtali8, M. Vanzini8, L.
Zanotti8, F. T. Avignone III9, R. J. Creswick9,
H. A. Farach9, C. Rosenfeld9, S. Cembrian10, I.
G. Irastorza9, A. Morales10 1Lawrence Berkeley
National Laboratory, 2University of California at
Berkeley 3Universita degli Studi
dellInsubria 4Universita di Firenze 5Laboratori
Nazionali del Gran Sasso 6Laboratori Nazionali di
Legnaro 7Leiden University 8Universita di
Milano-Bicocca 9University of South Carolina
10University of Zaragoza,
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(No Transcript)
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Detector concepts

• Temperature signal DT E/C ? 0.1 mK for E 1
  MeV

• Bias I ? 0.1 nA ? Joule power ? 1 pW
  ?Temperature rise ? 0.25 mK

• Voltage signal DV I ? dR/dT ? DT ? DV 1 mV
  for E 1 MeV

• Signal recovery time t C/G ? 0.5 s

• Noise over signal bandwidth (a few Hz) Vrms
  0.2 mV

Energy resolution (FWHM) ? 5 keV at 2500 keV
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Properties of 130Te as a DBD emitter
130Te presents several nice features
large phase space, lower background (clean
window between full energy and Compton edge of
208Tl photons)

• high natural isotopic abundance (I.A. 33.87
  )
• high transition energy ( Q 2528.8 1.3 keV )
  
• encouraging theoretical calculations for 0n-DBD
  lifetime
• already observed with geo-chemical techniques
• ( t 1/2 incl ( 0.7 - 2.7 ) ? 1021 y)

ltmngt ? 0.1 eV ? t ? 1026 y
0n-DBD half-life (y) for ltmngt 0.1
eV (different calculations)
Comparison with other candidates
Isotopic abundance ()
Transition energy (MeV)
5
1030
40
4
20
1027
3
0
2
1024
48Ca
76Ge
82Se
96Zr
100Mo
116Cd
130Te
136Xe
150Nd
48Ca
76Ge
82Se
96Zr
100Mo
116Cd
130Te
136Xe
150Nd
48Ca
76Ge
82Se
96Zr
100Mo
116Cd
130Te
136Xe
150Nd
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Evolution of the detectors
Mi DBD - II CUORICINO CUORE
Mi DBD - I
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CUORICINO sensitivity
Detector mass (kg)
Running time (y)
Isotopic abundance
Detector efficiency
1/2
a
M T
F0n 4.17 ? 1026 ?
? e
A
b G
Atomic mass
BKG (counts/keV/kg/y)
Energy resolution (keV)
Reasonable b 0.1 - G 5 keV
Pessimistic b 0.3 - G 10 keV
F0n 8.5 ? 1024 (T1 y)
F0n 3.5 ? 1024 (T1 y)
ltmngt ? 0.37 - 0.77 eV
ltmngt ? 0.24 - 0.50 eV
ltmngt (eV)
The lower bounds in ltmngt range (0.24 eV - 0.37
eV) are obtained with the same matrix elements
calculation used in this reference
H.V. Klapdor et al. claim 0.11 - 0.56 eV (0.39
eV c.v.) Mod. Phys. Lett. A 16 (2001) 2409
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Crystal Polishing February 2002
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Attaching thermistors to TeO2 crystals
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LBNL Roles
1999 Development of NTD Ge thermistors
2000 Assisted in construction of MiBeta
upgrade 2001 Polishing MiBeta and
Cuoricino Crystals 2002
Construction of Cuoricino 2003
Operation of CUORICINO Submission of
CUORE proposal 2004-5 Design clean
room for crystal fabrication Produce NTD Ge
Thermistors 2006? First
delivery of crystals for CUORE 2007?
Start of CUORE data taking
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CUORE sensitivity
Summarizing the BKG contributions

• Bulk contamination is not a problem ? ? 0.001
  counts/keV/kg/y

• Surface contamination is potentially dangerous,
  
• but the amount of Cu facing the detector will
  be reduced by a factor 10 -100
• with respect to now ? ? 0.01 - 0.001
  counts/keV/kg/y

Pessimistic estimation b 0.01 - G 5 keV
F0n 1.1 ? 1026 ? ( Ty )1/2
ltmngt ? 66 - 140 meV ? ( Ty )1/4
Optimistic estimation b 0.001 - G 5 keV
F0n 3.6 ? 1026 ? ( Ty )1/2
ltmngt ? 37 - 76 meV ? ( Ty )1/4
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CUORE cost estimation
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The Majorana Project

• Collaborators
• PNNL
• U of South Carolina
• TUNL
• ITEP
• Dubna
• NMSU
• U of Washington

• Industrial Partners
• ORTEC
• Canberra
• XIA
• MOXTEK
• ECP

See http//majorana.pnl.gov for latest project
info
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Majorana Highlights

• Neutrinoless double-beta decay of 76Ge
  potentially measured at 2038.6 keV
• Rate of 0n mode determines Majorana mass of ne
• as low as 0.02-0.07 eV
• Requires
• Deep underground location
• 20M enriched 85 76Ge
• 210 2kg crystals, 12 segments
• Advanced signal processing
• 20M Instrumentation
• Special materials (low bkg)
• 10 year operation

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Pulse-Shape Discrimination and Segmentation for
0n bb-Decay

• Major cosmogenic backgrounds (60Co, 68Ge)?require
  multiple depositions to reach 2 MeV
• 0n bb-decay is essentially a single-site process
• Pulse-Shape Discrimination (PSD) radial
• Single-site depositions create current pulses
  populating a small area of a well-chosen
  parameter space.
• Multiple-site depositions are linear combinations
  of single-site current pulse-shapes and populate
  a larger area of this experimentally verified
  parameter space.
• Segmentation axial and azimuthal
• Single-site depositions are nearly always
  contained in a single detector segment.
• Multiple-site depositions usually leave energy in
  more than one segment, with a probability
  depending on segment geometry.

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Parameter-Space Pulse Shape Discrimination

• Sensitive to radial separation of depositions
• Self-calibration allows optimal discrimination
  for each detector
• Discriminator can be recalibrated for changing
  electronic variables
• Method is computationally cheap, no computed
  pulse libraries needed

Single site distribution
Multiple site distribution
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Detector Segmentation

• Sensitive to axial and azimuthal separation of
  depositions
• Perkin-Elmer design with six azimuthal and two
  axial contacts has low risk
• Projected efficacy of this design is excellent
  with expected backgrounds

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Moscow-Heidelberg 76Ge
Contributed paper B7-2 This Meeting
Seeing is believing
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Projected SensitivityGround State

• GIVEN
• Background at 2038 keV 0.2 cts/keV/kg/y
• 68Ge decay 10x reduction
• 60Co decay/self shielding/less copper mass 2x
  reduction
• 500 kg 86 76Ge x 10 years
• PSDSegmentation FOM 1.6 x 2.4 3.8
• RESULT
• T0n 4.0 x 1027 y
• ltmngt 0.020 0.068 eV
• What is background was zero? (4.8 counts less)
• T0n 2.0 x 1028 y
• ltmngt 0.009 0.031 eV

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Detector RD Motivations
The Nygren View

• Double beta-decay experiments are among highest
  priority scientific objectives
• Experiments which measure energy only are
  vulnerable to backgrounds
• Backgrounds have been serious.
• Several nuclei must be studied to reduce
  systematic errors in interpretation
• Several experiments are justifiable

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Next Generation

• Requirements for next generation energy-only
  experiments are daunting
• Hundreds of kg of stuff are needed!
• Backgrounds must be reduced by 10x, x gt3 ?
• Background limited experiments t1/4 - bad!
• Many years to establish viability
• How to establish scaling practicality...

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Alternate Idea Use ?? Topology

• ?? topology in magnetic field is distinctive
• Rejection of ?,e backgrounds due to
• Compton scatter, pair production, nuclear decay
• ? decays, neutron scatters, ?, wimps,.
• ?
• Radio-purity issues may be much less important

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Topologies - with magnetic field
Compton
Pair production (V shape)
?? Decay Dingbat
?
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Potentially Stronger Result

• Experimental result is an energy spectrum
• contains both 2?- and 0?-?? decay events,
• contains little or no background
• Energy resolution expected to be 1
• Visible 0? peak at endpoint if ? is Majorana

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Concept

• Develop imaging technique based on
• Image capture by ion drift in insulating liquid
• Strong magnetic field to visualize ?? topology
• Track lengths 1.5 cm (Q of decay, liquid)
• Low rate experiment permits slow drift velocity
• V 2 cm/second expected _at_ 4 kV/cm
• Spatial resolution of 20 ??m expected _at_ 5 cm
• ?? new kind of TPC-like detector

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Many Challenging Issues...

• Will topology offer useful discrimination in the
  presence of multiple scattering ?
• Which isotope?
• Do isotopes of interest exist in insulating
  liquid form with acceptable chemistry?
• Do ions display unique drift velocities?
• Can practical detector modules be made?

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Can Magnetic Bending dominate Multiple
Scattering?

• Multiple scattering degrades topology -
• Rough Monte Carlo is encouraging.
• Is overall efficiency high enough to be useful?
• How high a magnetic field?
• 2T seems OK, (event radius 3mm)
• Algorithmic strategies to discard kinks due to
  hard scatters must be developed

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Which isotope?

• 48Ca is ideal
• Lowest Z (20), highest Q (4.3 MeV)
• Natural abundance very low 0.2 ? problem!
• Few insulating liquids with Ca ? challenge!
• Other possibilities
• 96Zr (2.8 abundance), Z40 , Q 3.35 MeV
• 82Se (8.7 abundance), Z34 , Q 3.0 MeV

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Ion Drift in Insulating Liquids

• No basic reason why low drift velocity Vd is
  inappropriate for low rate experiments
• Is ion drift velocity Vd single-valued?
• Solvation may introduce range of values...
• Ion yield may be 1 ion pair per 200 eV
• ? 21,000 ion pairs per 0? decay
• ? 200 ion pairs per measurement along track

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Detector Concept

• Small signal (200e) drives readout concept
• ?
• pixellated readout needed to achieve low noise
• Low Vd ? low bandwidth electronics
• ?
• low readout noise is possible

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Detector Concept.
HV 20 kV
Basic Module holds 1 liter of insulating liquid
Pixel size is 100 x 100 ?m2
Drift ? B field ?
Pixellated readout plane
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Summary

• Many issues to resolve, but
• Potentially very powerful approach
• Detector RD issues not costly to explore
• Other next-generation techniques not shown to
  have adequate background rejection
• LBNL should support detector RD!