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The COBRA Experiment

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  1. The COBRA Experiment Henric Krawczynski (Washington Univ. in St. Louis)for the COBRA Collaboration • Introduction to COBRA. • CZT Detectors. • Backgrounds & Sensitivity. • Plans and Requirements.

  2. COBRA Collaboration (Zuber et al.) University of Sussex University of Bratislava University of Warwick University of Liverpool Rutherford Appleton Lab. University of Jyvaskyla University of Birmingham University of York TU Dresden University of La Plata University of Dortmund MRC Freiburg Technical University Prague Laboratori Nazionali del Gran Sasso Still expanding. Washington University in St. Louis Idaho National Laboratory Observer status: University of Surrey (UK), University of Hamburg (Germany), Jagellonian University (Poland), Louisianna State University (USA), Technical University Dresden (Germany), Daresbury Laboratory (UK), Los Alamos National Laboratory (USA).

  3. 116Cd Double Beta Decay of 116Cd 116Cd Q-value: 2.809 MeV. Natural 116Cd abundance: 7.49% 116Cd (+ 130Te?) enrichment. F. Simkovic, ILIAS DBD meeting, Valencia 2006, see also:E. Caurier and J. Menendez and F. Nowacki and A. Poves, nucl-th/0709.2137

  4. COBRA Strengths • Source = detector. • Semiconductor. • Room temperature. • Modular design. • Industrial development of CdZnTe detectors. • 116Cd Q-value: 2.809 MeV. • Sub-mm Tracking („Solid state TPC“).

  5. 111cm3 COBRA (Cadmium-Telluride O-neutrino double-Beta Research Apparatus) Based on Arrays of CdZnTe semiconductor detectors: K. Zuber, Phys. Lett. B 519,1 (2001) 122cm3 0.822cm3 0.522cm3 0.222cm3

  6. CZT Detectors - Energy Resolution 1.522cm36 cm3 = 35 gr. Zhong, Krawczynski et al.

  7. Status of COBRA Prototype Experiment 64 Detector Array at Gran Sasso National Laboratory: Oct. 2007 64 detectors operational!

  8. Preliminary Results With 4x4 Detector Layer About 8 kg days (x2 more than published, T. Bloxham et al. Phys. Rev. C, 76, 025501 (2007)

  9. Recent Improvements: Substantial Background Reduction • Problems: • Passivation paint. • Radon. Expected background index: 150  < 1 cts keV-1 kg-1 yr-1.

  10. Simulations: ~3x10-7 counts/year/kg/keV in the crystals. <1 neutron per year in 420 kg experiment. D. Stewart et al., NIMA, 571, 651 (2007). Background Estimate Simulations of external, internal, cosmogenic, and  backgrounds: background index: 10-4-10-3cts keV-1 kg-1 yr-1.

  11. 50 meV COBRA Sensitivity Background free: Background limited:

  12. CZT Detectors - Spatial Resolution 1.3mm pixel pitch Washington Univ. 50 m squares Development of ≥0.5 cm thick detectors with 200 micron spatial resolution and multiplexed readout.

  13. Additional Background Rejection Through Event Tracking • Massive BG reduction by particle ID , 200m pixels (see e.g. Bloxham & Freer, NIMA, 572,2, 722 (2007)): 0  ~15m 1-1.5mm • eg. Could achieve nearly 100% identification alphas and of 214Bi beta events (214Bi  214Po  210Pb).

  14. COBRA: a solid state  experiment with unique capabilties! Next steps (continued R&D): • Reduce background for 64-detector experiment. • Detector development: • Radiochemical cleaning (extraction chromatography). • Use of Cd enriched to >90% with 116Cd. • 200 m spatial resolution. • Full tradeoff study coplanar grid vs. pixelated detectors, test of shielding and background suppression methods in test beams and underground. Towards a large-scale experiment: • 2010/2011: Finalize design. • 2012: Construction of experiment in layers of 40x40 detectors. DUSEL Requirements: • COBRA: compact, no crygenic cooling, little liquid chemicals. • Multiple campuses advantageous. • Weekly seminar to engender interaction of scientists from different disciplines.

  15. Results from Background Simulations External: Internal: Cosmogenics: