K. Zuber, Uni. Sussex
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Transcript of K. Zuber, Uni. Sussex
K. Zuber, Uni. Sussex
Status of COBRA
IDEA Meeting, Zaragoza 7 Nov. 2005
Contents
• Introduction• Current status of
COBRA• The 64 detector
array• Longer term
planning• Summary
C0BRA
Use large amount of CdZnTe Semiconductor Detectors
Array of 1cm3
CdTe detectors
K. Zuber, Phys. Lett. B 519,1 (2001)
Cobra - The peopleC. Gößling, H. Kiel, D. Münstermann, S. Oehl, T. Villett
University of DortmundJ. Dawson, C. Montag, D. Polzaird, C. Reeve, J. Wilson, K. Zuber
University of Sussex
+ further interested institutes
Laboratori Nazionali del Gran SassoM. Junker
University of WarwickP.F. Harrison, B. Morgan, Y. Ramachers, D. Stewart
T. Bloxham, M. Freer
P. Seller
B. Fulton, A. Smith, R. Wadsworth
A. Boston, P. Nolan
University of Birmingham
University of Liverpool
University of York
Rutherford Appleton Laboratory
COBRA 2005
some are missing...
Isotopes
Zn70 0.62 1001 ß-ß-Cd114 28.7 534 ß-ß-Cd116 7.5 2805 ß-ß-Te128 31.7 868 ß-ß-Te130 33.8 2529 ß-ß-Zn64 48.6 1096 ß+/ECCd106 1.21 2771 ß+ß+Cd108 0.9 231 EC/ECTe120 0.1 1722 ß+/EC
nat. ab. (%) Q (keV) Decay mode
COBRA: CdZnTe semiconductors
Level schemes
Quite a few lines...
++ - modes
• (A,Z) (A,Z-2) + 2 e+ (+2e) ++ • e- + (A,Z) (A,Z-2) + e+ (+2e ) +/EC
• 2 e- + (A,Z) (A,Z-2) (+2e) EC/EC
Important to reveal mechanism if 0 is discoveredEnhanced sensitivity to right handed weak currents
(V+A)
n
n
p
pe
eIn general:
Q-4mec2
Q-2mec2
Q
Double charged higgs bosons,R-parity violating SUSY couplings,leptoquarks...
Neutrino mass vs. right handed currents++++ +++∝ RRLRRLLL JjJjJjJjH ληκint
€
λ,η <<1
<m> (eV)
<λ>
Possible evidence
M. Hirsch et al., Z. Phys. A 347,151 (1994)
EC/ß+
Advantages
• Source = detector
• Semiconductor (Good energy resolution, clean)
• Room temperature
• Tracking („Solid state TPC“)
• Modular design (Coincidences)
• Industrial development of CdTe detectors
• Two isotopes at once
• 116Cd above 2.614 MeV
Contents
• Introduction• Current status of
COBRA• The 64 detector
array• Longer term
planning• Summary
Running periods
• Running at LNGS since February 2004
• Scheme driven by money/manpower
• CAMAC DAQ - 4 detector prototype
• CAMAC DAQ - 4 detector prototype mod.
• VME DAQ - 4 detector prototype modified
Background
• Cosmogenics
• neutrons
116Cd (Q=2805 keV)
• 2
113Cd (nth,)114Cd
Measurement: E. Porras et al., NIM B 111, 325 (1996)
• Alphas, Betas, Gammas
• muon induced neutrons
2 - decay
+ Tracking option
€
F =8Q(ΔE /Q)6
me
= 3.7*10−10
S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci. 2002
Energy resolution important semiconductor
Fraction of 2 in 0 peak:
Signal/Background:
4331
02/1
22/1 ==
TT
FBS
yrsT 1922/1 102.3 ×=
yrsT 2602/1 102×=
2 is ultimate, irreducible background
The 2x2 prototype
4 naked 1cm3 CdZnTe
more than 2.5 kg x days of data
Setup installed at Gran Sasso Underground Laboratory
NeutronsWorry (if not enriched in 116Cd): 113Cd (nth,)114Cd
MCNP simulation of the full set-up
Calibration
2.4% energy resolution at 2614 keV
Much better ones available
A little bit of cooling helps
Comparison of measurements
0.5 cm3, surface, no shielding
„old“ prototype, LNGS, no shielding
„old“ prototype, LNGS, shielding, no veto
The background model
Input: Pertinax (grid, base), detectors, paint and copper
Currently limiting background: Passivation paint on detectors
Strategies
• We started a long term R&D with eV-Products to find another passivation (they have alternatives)
• Alternative providers not using the paint(Freiburg Material Research Centre)
Redesigned prototype
Delrin holder and kapton foilScalable design for larger masses
New versus old prototype
Measuring time: 2630 hours , about 0.71 kg x days, Det1 only
Physics - 113Cd
T1/2 = (8.2 ± 0.2 (stat.) +0.2-1.0 (sys)) 1015 yrs
113Cd one of only three 4-fold forbidden -emitters known in nature
C. Goessling et al., nucl-ex/0508016, acc. by Phys. Rev. C
First results
1/2 close to 1020 years obtained
70Zn 1.3 x 1016 2.9x1017
116Cd 8.0 x1018 1.1x1019
130Te 3.3x1019 8.2x1019
106Cd 0+ EC 3.8x1017 1. 6x1018
64Zn 0+ EC 2.8x1016 2.6x1017
120Te 0+EC 2.2x1016 9.3x1016
0
NPA723
NPA 723
Current
Current
EC-modes
H.Kiel, D. Münstermann, K. Zuber, Nucl. Phys. A 723,499 (2003)
Current results are preliminary
CoincidencesAim: Coincidences among crystals should significantly reduce gamma background
About 0.2 % ofevents are coincidences
Array too small to prove power of coincidences Larger Array
5 10 15 20 25 30
5
10
15
20
25
30
x
y
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
2000keV
2614 keV gamma (MC)
Contents
• Introduction• Current status of
COBRA• The 64 detector
array• Longer term
planning• Summary
The 64 detector arrayAim for next 2 years: The next step towards a large scale experiment,Scalable modular design, explore coincidences
Include:CoolingNitrogen flushing
Mass is factor 16 higher,about 0.5 kg CdZnTe
Physics: - Can access2ECEC in theoreticallypredicted region-Precision measurement of 113Cd- New limitsAll detectors are at Dortmund
Signatures - +/EC
High granularity
A lot of patterns,interesting to investigate
Contents
• Introduction• Current status of
COBRA• The 64 detector
array• Longer term
planning• Summary
The solid state TPC
Single electron spectra
Angular correlationcoefficient
Introduce tracking properties by using segmentedor pixellated electrodes and pulse shape analysis
First own measurements
Two detectors: 4x4 pixel , 2mm x 2mm16x16 pixel, 1.6 mm x 1.6 mm
- plot Source location
Two pixel events
Pixellated detectors
3D - Pixelisation:
Solid state TPC
Nobody said it was going to be easy, and nobody was right
George W. Bush
Back of the envelope
1/2 = ln2 • a • NA• M • t / N (T) ( Background free)
50 meV implies half-life measurements of 1026-27 yrs
1 event/yr you need 1026-27 source atoms
This is about 1000 moles of isotope, implying 100 kg
Now you only can loose: nat. abundance, efficiency, background, ...
Dimension it right!
116Cd
116In
116Sn
A real time low-energy solar neutrino experiment?
Threshold energy: 464 keV
7Be contribution g.s. alone: 227 SNU
= 14s
K. Zuber, Phys. Lett. B 571,148 (2003)
e
ee
Current idea: 40x40x40 CdZnTe detectors = 420 kg, enriched in 116Cd
Sensitivity
50 meV
Summary
• COBRA plans to use a large amount of CdZnTe semiconductors for double beta searches
• Collaboration of about 25 people established• Currently preparing a 64 detector array (about 0.5
kg), to be installed at LNGS end of 2005• Design changed to allow easy upgrade to larger
scales• Work on signal enhancer/active veto and pixellated
detectors has started• Progress is fast
Einstein was right