Transcript Cobra
K. Zuber, Uni. Sussex IDEA Meeting, Zaragoza 7 Nov. 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. Polzaird, 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 Level schemes Quite a few lines... ++ - modes n p e In general: Double charged higgs bosons, R-parity violating SUSY couplings, leptoquarks... n • (A,Z) (A,Z-2) + 2 e+ (+2e) p e ++ Q-4mec2 • e- + (A,Z) (A,Z-2) + e+ (+2e ) +/EC Q-2mec2 • 2 e- + (A,Z) (A,Z-2) (+2e) EC/EC Q Important to reveal mechanism if 0 is discovered Enhanced sensitivity to right handed weak currents (V+A) Neutrino mass vs. right handed currents H int jL J L jL J R jR J L jR J R <> EC/ß+ , 1 Possible evidence <m> (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“) 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 116Cd (Q=2805 keV) • Alphas, Betas, Gammas • Cosmogenics Measurement: E. Porras et al., NIM B 111, 325 (1996) • neutrons 113Cd (nth,)114Cd • 2 • muon induced neutrons 2 - decay 2 is ultimate, irreducible background Energy resolution important semiconductor 8Q(E /Q) 6 10 F 3.7 *10 Fraction of 2 in 0 peak: me S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci. 2002 Signal/Background: S 1 T12/ 2 433 0 B F T1/ 2 T12/ 2 3.2 1019 yrs T10/2 21026 yrs + Tracking option The 2x2 prototype Setup installed at Gran Sasso Underground Laboratory 4 naked 1cm3 CdZnTe more than 2.5 kg x days of data Neutrons Worry (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 Scalable design for larger masses Delrin holder and kapton foil New versus old prototype Measuring time: 2630 hours , about 0.71 kg x days, Det1 only Physics 113Cd 113Cd one of only three 4-fold forbidden -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) 0 NPA 723 Current 70Zn 1.3 x 1016 2.9x1017 116Cd 8.0 x1018 1.1x1019 130Te 3.3x1019 8.2x1019 EC-modes NPA723 Current 106Cd 0+ EC 3.8x1017 1. 6x1018 64Zn 0+ EC 2.8x1016 2.6x1017 120Te 0+EC 2.2x1016 9.3x1016 Current results are preliminary T1/2 close to 1020 years obtained Coincidences Aim: Coincidences among crystals should significantly reduce gamma background 2614 keV gamma (MC) 2000keV 1 30 0.9 25 0.8 0.7 20 0.6 y 0.5 15 0.4 10 About 0.2 % of events are coincidences 0.3 0.2 5 0.1 5 10 15 x 20 25 30 0 Array too small to prove power of coincidences Larger Array Contents • Introduction • Current status of COBRA • The 64 detector array • Longer term planning • Summary 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 2ECEC in theoretically predicted region -Precision measurement of 113Cd - New limits 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 Introduce tracking properties by using segmented or pixellated electrodes and pulse shape analysis Single electron spectra Angular correlation coefficient First own measurements Two detectors: 4x4 pixel , 2mm x 2mm 16x16 pixel, 1.6 mm x 1.6 mm Two pixel events - plot Source location Pixellated detectors Solid state TPC 3D - Pixelisation: Nobody said it was going to be easy, and nobody was right George W. Bush Back of the envelope T1/2 = ln2 • a • NA• M • t / N (tT) ( 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! Current idea: 40x40x40 CdZnTe detectors = 420 kg, enriched in 116Cd A real time low-energy solar neutrino experiment? e e 116Cd 116In Threshold energy: 464 keV e 7Be contribution g.s. alone: 227 SNU t = 14s 116Sn K. Zuber, Phys. Lett. B 571,148 (2003) 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