1. Status of COBRA 6 th SNOLAB Workshop, 22.8.2007 Picture courtesy farine@snolab.ca

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

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

4. V.K.B. Kota, priv. comm. 116 Cd comes of best...

5. 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 2.614 MeV

6. COBRA collaboration University of Surrey (UK), University of Hamburg (Germany), Technical University Prague (Tschech Rep.), Jagellonian University (Poland), Louisianna State University (USA) University of Dortmund University of Sussex Laboratori Nazionali del Gran Sasso University of Warwick University 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 University of La Plata

7. COBRA at LNGS COBRA Since april 2007 2004-march 2007

8. world best First COBRA Double beta results T. Bloxham et al., arXiv:0707.2756,, Phys. Rev. C 76, 025501 (2007) PertinaxCopperCZTWax Based on 4 detectors, total of 4.34 kg x days

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

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

11. The first layer Installed at LNGS in april 2006, world wide largest array of this type of detector, remaining 48 will be installed autumn 2007

12. The first layer - some spectra Cd-113 beta decay with half-life of about 10 16 yrs

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

14. 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 !

15. New passivation (4 detectors) Sample measurements at ICP-MS @ 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

16. 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

17. Sensitivity 50 meV

18. Energy Resolution Only electron signal read out (CPG technology) Possible improvements: cooling, new grids Better detectors are available  E = 1.9% @ 2.8MeV =2.9% @ 662keV Resolution of  =0.8% at 2.8 MeV

19. 2  - decay S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci. 2002 Energy resolution (FWHM) important  semiconductor Fraction of 2  in 0  peak: Signal/Background: 2  is ultimate, irreducible background

20. The solid state TPC Energy resolutionTracking Pixelated CdZnTe detectors Massive background reduction Positive signal information

21. Pixelisation - 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 = 164.3  s Beta with endpoint 3.3MeV  = 1 pixel,  and  = several connected pixel,  = some disconnected p.

22. Rejection power of pixels First look on rejection power Suggests a background reduction of 1000! T. Bloxham, M. Freer, Nucl. Inst. Meth. A 572, 722 (2007) Likelihood using: -Number of pixels - spatial separation - energy loss (dE/dx)

23. Pixelisation - II Running 256 pixel det with ASIC, 1.6mm pixel size crystal ASIC readout 122 keV 136 keV Single pixel 57 Co spectrum Additional 16 pixel detector with conventional readout running

24. Pixel detectors - next step 64 pixel detectors 2x2x0.5 cm 3 Pixel electrodes will be replaced by 200  m pixels, mask in hand By end 2007 we‘ll have two high resolution pixel detectors

25. Pixellated detectors 2D - Pixelisation on both electrodes Solid state TPC

26. 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

27. Summary COBRA is a new approach to double beta decay using CdZnTe semiconductors 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 Revived interest in neutrinoless double EC Possible interest to come to SNOLAB early 201x Progress is fast....