Status of COBRA K. Zuber, Univ. of Sussex Blaubeuren, July 2007

COBRA Use large amount of CdZnTe Semiconductor Detectors Array of 1cm 3 CdZnTe detectors K. Zuber, Phys. Lett. B 519,1 (2001)

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

COBRA collaboration University of Surrey (UK), University of Hamburg (Germany), Jagellonian University (Poland),Louisianna State University (USA) University of Dortmund University of Sussex Laboratori Nazionali del Gran Sasso University of WarwickUniversity of Birmingham University of Liverpool University of York Rutherford Appleton Laboratory University of Bratislava Washington University at St. Louis Material Research Centre Freiburg More welcome University of Jyvaskyla

COBRA at LNGS COBRA Since april march 2007

world best First COBRA Double beta results T. Bloxham et al., submitted PertinaxCopperCZTWax Based on 4 detectors, total of 4.34 kg x days

Redesigned prototype Delrin holder and kapton foil Scalable design for larger masses

The 64 array - the next step 4x4x4 detector array = 0.42 kg CdZnTe semiconductors

The 64 detector array The next step towards a large scale experiment, Scalable modular design, explore coincidences Worldwide largest experiment of 1cm 3 CPG detectors Mass factor 16 higher, about 0.42 kg CdZnTe Physics: - Can access 2 ECEC in theoretically predicted region -Precision measurement of 113Cd - New limits 70 detectors in total available/characterised

The first layer Installed at LNGS in april 2006

The first layer - some spectra Cd-113 beta decay with half-life of about yrs

The first layer - Coincidences Just starting to analyse/understand the power of that.. Preliminary Coincidences around Det 7 Example: 3-coincidence Powerful tool!!! Coincidences

Example: 130 Te 1 st excited state 1.1 Detector with 2530 keV 2.1 Detector with 1994 keV 3.2 Detectors (One with 1994 keV, one with 536 keV)) 4.2 Detectors (One with 1994 keV, two sum up to 536 keV) Have performed a search for mode 3 in 4.2 kg x days and found no event !

Ex. 2: 106 Cd 0 ECEC with 2 photons Signature: Triple coincidence : Middle detector (X-rays),two more detectors in a line with E  and (Q-X-rays- E  ) Very likely background free! F. Simkovic et al. 11 22

New passivation (4 detectors) Sample measurements at LNGS suggest improvement of about 3 orders of magnitude Monte Carlo expectation Paint contribution at 2.8 MeV: about 0.2 counts/keV/kg/yr Major background so far: Red paint on detector surface

New passivation Very preliminary: At least a factor 10 better, lot of construction work around COBRA at LNGS, no coincidences, no nitrogen flushing... Around 10 counts/keV/kg/yr

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.

Rejection power of pixels First look on rejection power Suggests a background reduction of 1000! T. Bloxham, M. Freer, Nucl. Inst. Meth. A (2007) Likelihood using: -Number of pixels - spatial separation - energy loss (dE/dx)

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

A. Poves (yesterday): 116 Cd most convenient, T 1/2 = 2.9 x10 26 for 50meV Uncertainties in nuclear matrix elements, example 116 Cd V. Rodin et alnucl-th/ , Nucl. Phys. A 766,107 (2006) V. Rodin et al., nucl-th/ , Nucl. Phys. A 766,107 (2006)

Sensitivity (conservative) 50 meV Assume BG limited from beginning

2  - decay S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci Energy resolution (FWHM) 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

COBRA for solar neutrinos - King COBRA 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

SNO+ - A 150 Nd double beta decay experiment

SNO+- 1 st collab. meeting More welcome!

Summary COBRA is a new approach to double beta decay using CdZnTe Follows two lines: Background identification and reduction (LNGS) and development of high resolution pixel-CZT Two major items for 2007: Finish the 64 array at LNGS in new location Two high resolution pixel detectors Progress is fast....

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