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 1cm 3 CdTe detectors K. Zuber, Phys. Lett. B 519,1 (2001)
Cobra - The people + further interested institutes 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) Decay mode 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+/EC Cd106 1.21 2771 ß+ß+ Cd108 0.9 231 EC/EC Te120 0.1 1722 ß+/EC
Quite a few lines...
β + β + - modes In general: Double charged higgs bosons, R-parity violating SUSY couplings, leptoquarks... (A,Z) (A,Z-2) + 2 e + (+2ν e ) n n p e p e β+β+ Q-4m e c 2 e - + (A,Z) (A,Z-2) + e + (+2ν e ) β+/ec 2 e - + (A,Z) (A,Z-2) (+2ν e ) EC/EC Q-2m e c 2 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 j L J + L + κj L J + R + ηj R J + L + λj R J + R EC/ß + <λ> λ,η <<1 Possible evidence <m n > (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 116 Cd above 2.614 MeV Tracking ( Solid state TPC )
Background 116 Cd (Q=2805 kev) Alphas, Betas, Gammas Cosmogenics Measurement: E. Porras et al., NIM B 111, 325 (1996) neutrons 2νββ 113 Cd (n th,γ) 114 Cd muon induced neutrons
2νββ - decay 2νββ is ultimate, irreducible background Energy resolution important semiconductor Fraction of 2νββ in 0νββ peak: F = 8Q( E /Q)6 m e = 3.7 *10 10 S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci. 2002 Signal/Background: S B 1 F T 2ν 1 /2 = = 0ν T1/2 433 2ν 19 T1 / 2 = 3.2 10 yrs 0ν 26 T1 / 2 = 2 10 yrs + Tracking option
The 2x2 prototype Setup installed at Gran Sasso Underground Laboratory 4 naked 1cm 3 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 cm 3, surface, no shielding old prototype, LNGS, no shielding old prototype, LNGS, shielding, no veto
Physics - 113 Cd 113 Cd one of only three 4-fold forbidden β-emitters known in nature T 1/2 = (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 25 20 15 10 About 0.2 % of events are coincidences 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 All detectors are at Dortmund Mass is factor 16 higher, about 0.5 kg CdZnTe 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? ν e 116Cd 116In e e τ = 14s Threshold energy: 464 kev 7Be contribution g.s. alone: 227 SNU 116Sn K. Zuber, Phys. Lett. B 571,148 (2003)
Sensitivity 50 mev
Single electron spectra The solid state TPC Introduce tracking properties by using segmented or pixellated electrodes and pulse shape analysis 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