Status of COBRA - SPring-8

K. Zuber, Uni. Sussex
NNR 05, Osaka 2-4.12. 2005
Status of COBRA
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)
+ further interested institutes
Cobra - The people
C. Gößling, H. Kiel, D. Münstermann, S. Oehl, T. Villett
University of Dortmund
J. Dawson, C. Montag, D. Palzeaird,
C. Reeve, J. Wilson, K. Zuber
University of Sussex
P.F. Harrison, B. Morgan, Y. Ramachers, D. Stewart
University of Warwick
A. Boston, P. Nolan
University of Liverpool
B. Fulton, A. Smith, R. Wadsworth
University of York
T. Bloxham, M. Freer
University of Birmingham
P. Seller
Rutherford Appleton Laboratory
M. Junker
Laboratori Nazionali del Gran Sasso
COBRA 2005
some are missing...
Isotopes
COBRA: CdZnTe semiconductors
nat. ab. (%) Q (keV)
Zn70
Cd114
Cd116
Te128
Te130
Zn64
Cd106
Cd108
Te120
0.62
28.7
7.5
31.7
33.8
48.6
1.21
0.9
0.1
1001
534
2805
868
2529
1096
2771
231
1722
Decay mode
ß-ßß-ßß-ßß-ßß-ßß+/EC
ß+ß +
EC/EC
ß+/EC
Quite a few lines...
β+β+ - modes
n
p
e
In general:
Double charged higgs bosons,
R-parity violating SUSY couplings,
leptoquarks...
n
• (A,Z) → (A,Z-2) + 2 e+ (+2νe)
p
e
β+β+ Q-4mec2
• e- + (A,Z) → (A,Z-2) + e+ (+2νe ) β+/EC Q-2mec2
• 2 e- + (A,Z) → (A,Z-2) (+2νe)
EC/EC Q
Important to reveal mechanism if 0νββ is discovered
Enhanced sensitivity to right handed weak currents (V+A)
Neutrino mass vs. right handed currents
H int ∝ jL J L+ + κjL J R+ + ηjR J L+ + λj R J R+
EC/ß+
<λ>
λ,η << 1
Possible
evidence
<mν > (eV)
M. Hirsch et al., Z. Phys. A 347,151 (1994)
Advantages
• Source = detector
• Semiconductor (Good energy resolution, clean)
• Room temperature
• Modular design (Coincidences)
• Two isotopes at once
• Industrial development of CdTe detectors
•
116Cd
above 2.614 MeV
• Tracking („Solid state TPC“)
Background
116Cd
(Q=2805 keV)
• Alphas, Betas, Gammas
• Cosmogenics
Measurement: E. Porras et al., NIM B 111, 325 (1996)
• neutrons
113Cd
(nth,γ)114Cd
• 2νββ
• muon induced neutrons
2νββ - decay
2νββ is ultimate, irreducible background
Energy resolution important → semiconductor
8Q(∆E /Q)6
−10
F
=
=
3.7
*10
Fraction of 2νββ in 0νββ peak:
me
S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci. 2002
Signal/Background:
S 1 T12/ ν2
=
= 433
0ν
B F T1/ 2
T12/ ν2 = 3.2 × 1019 yrs
T10/ ν2 = 2×10 26 yrs
+ Tracking option
The 2x2 prototype
Setup installed at Gran Sasso Underground Laboratory
4 naked 1cm3 CdZnTe
more than 3.2 kg x days of data
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
Physics - 113Cd
113Cd
one of only three 4-fold forbidden β-emitters known in nature
T1/2 = (8.2 ± 0.2 (stat.) +0.2 -1.0 (sys)) 1015 yrs
C. Goessling et al., nucl-ex/0508016, acc. by Phys. Rev. C
First results
H.Kiel, D. Münstermann, K. Zuber, Nucl. Phys. A 723,499 (2003)
COBRA
0νββ
70Zn
1.3 x 1016
2.7x1017
116Cd
8.0 x1018
1.2x1019
130Te
3.3x1019
5.7x1019
EC-modes
106Cd
64Zn
64Zn
Τ1/2 close to 1020
years obtained
Current
COBRA
0nb+
3.8x1017
EC +
0nb
2.8x1016
EC
0nECEC 2.2x1016
Current
2.5 x1019
5.1x1018
9.6x1016
Current results are preliminary
64Zn
limits world best
Coincidences
Aim: Coincidences among crystals should significantly reduce
gamma background
2614 keV gamma (MC)
30
About 0.2 % of
events are
coincidences
25
20
15
10
5
5
10
15
20
25
30
Array too small to prove power of coincidences → Larger Array
The 64 detector array
Aim for next 2 years: The next step towards a large scale experiment,
Scalable modular design, explore coincidences
Mass is factor 16 higher,
about 0.5 kg CdZnTe
All detectors are at Dortmund
Include:
Cooling
Nitrogen flushing
Physics:
- Can access
2νECEC in theoretically
predicted region
-Precision measurement
of 113Cd
- New limits
Signatures - β+/EC
High granularity
→
A lot of patterns,
interesting to
investigate
Dimension it right!
Current idea: 40x40x40 CdZnTe detectors = 420 kg, enriched in 116Cd
A real time low-energy solar neutrino experiment?
e
νe
116Cd
116In
Threshold energy: 464 keV
e
7Be contribution g.s. alone: 227 SNU
τ = 14s
116Sn
K. Zuber, Phys. Lett. B 571,148 (2003)
Sensitivity
50 meV
The solid state TPC
Introduce tracking properties by using segmented
or pixellated electrodes and pulse shape analysis
Single electron spectra
Angular correlation
coefficient α
First own measurements
Two detectors:
4x4 pixel , 2mm x 2mm
16x16 pixel, 1.6 mm x 1.6 mm
Two pixel events
θ - ϕ plot
Source
location
Pixellated detectors
We have two 2D pixellated detectors running
Solid state TPC
3D - Pixelisation:
Nobody said it was going to be easy, and nobody was right
George W. Bush
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