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 1cm 3 CdTe detectors K. Zuber, Phys. Lett. B 519,1 (2001)

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 + further interested institutes Laboratori Nazionali del Gran Sasso M. Junker University of Warwick P.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 nat. ab. (%)Q (keV)Decay mode COBRA: CdZnTe semiconductors

Level schemes

Quite a few lines...

 +  + - modes (A,Z)  (A,Z-2) + 2 e + (+2 e )  +  + e - + (A,Z)  (A,Z-2) + e + (+2 e )  +/EC 2 e - + (A,Z)  (A,Z-2) (+2 e ) EC/EC Important to reveal mechanism if 0  is discovered Enhanced sensitivity to right handed weak currents (V+A) n n p p e e In general: Q-4m e c 2 Q-2m e c 2 Q Double charged higgs bosons, R-parity violating SUSY couplings, leptoquarks...

Neutrino mass vs. right handed currents (eV) 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 116 Cd above 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 116 Cd (Q=2805 keV) 2  113 Cd (n th,  ) 114 Cd Measurement: E. Porras et al., NIM B 111, 325 (1996) Alphas, Betas, Gammas muon induced neutrons

2  - decay + Tracking option S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci Energy resolution important  semiconductor Fraction of 2  in 0  peak: Signal/Background: 2  is ultimate, irreducible background

The 2x2 prototype 4 naked 1cm 3 CdZnTe more than 2.5 kg x days of data Setup installed at Gran Sasso Underground Laboratory

Neutrons Worry (if not enriched in 116 Cd): 113 Cd (n th,  ) 114 Cd 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 cm 3, 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 foil Scalable design for larger masses

New versus old prototype Measuring time: 2630 hours, about 0.71 kg x days, Det1 only

Physics Cd T 1/2 = (8.2 ± 0.2 (stat.) (sys)) yrs 113 Cd one of only three 4-fold forbidden  -emitters known in nature C. Goessling et al., nucl-ex/ , acc. by Phys. Rev. C

First results  1/2 close to years obtained 70 Zn1.3 x x Cd8.0 x x Te3.3x x Cd 0  + EC 3.8x x Zn 0  + EC 2.8x x Te 0  + EC 2.2x x  NPA723 Current EC-modes H.Kiel, D. Münstermann, K. Zuber, Nucl. Phys. A 723,499 (2003) Current results are preliminary

Coincidences Aim: Coincidences among crystals should significantly reduce gamma background About 0.2 % of events are coincidences Array too small to prove power of coincidences  Larger Array 2614 keV gamma (MC)

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 Include: Cooling Nitrogen flushing Mass is factor 16 higher, about 0.5 kg CdZnTe Physics: - Can access 2 ECEC in theoretically predicted region -Precision measurement of 113Cd - New limits All 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 correlation coefficient  Introduce tracking properties by using segmented or pixellated electrodes and pulse shape analysis

First own measurements Two detectors: 4x4 pixel, 2mm x 2mm 16x16 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 N A M t / N  (   T) ( Background free)  50 meV implies half-life measurements of yrs 1 event/yr you need 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 116SnA 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 e e 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