COBRA Kai Zuber University of Sussex 5 th SNOLAB Workshop,

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 2006 some are missing...

Isotopes nat. ab. (%)Q (keV)Decay mode COBRA: CdZnTe semiconductors

 +  + - 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...

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

The 2x2 prototype 4 naked 1cm 3 CdZnTe more than 4.3 kg x days of data,stopped March 2006 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

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., Phys. Rev. C 72, (2005)

Latest Limits world best PRELIMINARY

Contents Introduction Current status of COBRA The 64 detector array Longer term planning Summary

The first layer Installed at LNGS about three month ago

Coincidences – 214 Bi T 1/2 = 162 ± 19  s Can exclude backgrounds through timing coincidence 214 Bi  214 Po  210 Pb 7.7MeV alpha half-life =  s Beta with endpoint 3.3MeV

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)

New passivation Raw data Very preliminary: At least a factor 10 better, lot of construction work around COBRA at LNGS, no coincidences, no nitrogen flushing... Cd116

Contents Introduction Current status of COBRA The 64 detector array Longer term planning Summary

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,...

Cd116- Matrix elements =0.4eV V. Rodin et alnucl-th/ , Nucl Phys. A 2006 V. Rodin et al., nucl-th/ , Nucl Phys. A 2006

Sensitivity 50 meV

2  - decay 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

Energy Resolution Only electron signal read out (CPG technology) Possible improvements: cooling, new grids Better detectors are available  E = 2.8MeV 662keV Resolution of  =0.8% at 2.8 MeV

Dimension it right! 116Cd 116In 116SnA real time low-energy solar neutrino experiment? Threshold energy: 464 keV 7Be contribution gs. 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

The solid state TPC Energy resolutionTracking Pixellated CdZnTe detectors Massive background reduction Positive signal information

Pixellisation - I Massive BG reduction by particle ID, 200  m pixels (example simulations) : eg. Could achieve nearly 100% identification of 214 Bi events ( 214 Bi  214 Po  210 Pb). 0   1-1.5mm ~15  m 3 MeV  7.7MeV  life-time =  s Beta with endpoint 3.3MeV  = 1 pixel,  and  = several connected pixel,  = some disconnected p.

Pixellisation - II Tests of 16×16 1.6mm pixel detectors crystal ASIC readout 122 keV 136 keV

Pixellated detectors 3D - Pixelisation: We have two 2D pixellated detectors running

Nobody said it was going to be easy, and nobody was right George W. Bush

Shielding and Veto Simulated LNGS neutron flux ~3x10 -7 counts/year/kg/keV in the crystals. <1 neutron per year!<1 neutron per year! (in detectors) Size = 18.4 m 3 Mass = kg D. Stewart et al., submitted to Nucl. Inst. Meth. A detectors

And many more things going on Red = 24°C Blue = 10°C T-measurement Pulse shape analysis Thermal n-capture PL: Zn-content nm

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), installation at LNGS started spring 2006 Design changed to allow easy upgrade to larger scales Work on signal enhancer and pixellated detectors has started New german grant application successful, UK and US grant applications in preparation Around 2009/10 TDR for large experiment