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K. Zuber, Uni. Sussex

K. Zuber, Uni. Sussex. Erice School, 16-23 Sep. 2005. Status of COBRA. Contents. Introduction Current status of COBRA The 64 detector array Longer term planning Summary. Heidelberg -Moscow. Five Ge Diodes (mass 10.9 kg) Isotopical enriched ( 86%) in 76 Ge

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K. Zuber, Uni. Sussex

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  1. K. Zuber, Uni. Sussex Erice School, 16-23 Sep. 2005 Status of COBRA

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

  3. Heidelberg -Moscow • Five Ge Diodes (mass 10.9 kg) • Isotopical enriched ( 86%) in 76Ge • lead shield and nitrogen purgingPeak at 2039 keV H.V. Klapdor-Kleingrothaus et al, Europ. Phys. J. A 12, 147 (2001) T1/2 > 1.9 x 1025 yr (90% CL) m < 0.35 eV Evidence ? Subgroup of collaboration T1/2 = 0.6 - 8.4 x 1025 yr m = 0.17 - 0.63 eV H.V. Klapdor-Kleingrothaus et al, Phys. Lett. B 586, 198 (2004)

  4. Nuclear matrix elements measured quantity quantity of interest 1 / T1/2 = PS * NME2 * (m / me)2 The big unknown Started worldwide effort for a coherentprogram to reduce NME uncertainties(hopefully) down to 30%, summary report available soon m = |  Uek2 mk | Beware of: http://www.ippp.dur.ac.uk/0NU2B/2005.html

  5. C0BRA Use large amount of CdZnTe Semiconductor Detectors Array of 1cm3 CdTe detectors K. Zuber, Phys. Lett. B 519,1 (2001)

  6. + further interested institutes 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 P.F. Harrison, B. Morgan, Y. Ramachers, D. Stewart University of Warwick A. Boston, P. Nolan University of Liverpool B. Fulton, A. Smith, R. Wadsworth University of York T. Bloxham, M. Freer University of Birmingham P. Seller Rutherford Appleton Laboratory M. Junker Laboratori Nazionali del Gran Sasso

  7. COBRA 2005 some are missing...

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

  9. ++ -modes n p e In general: Double charged higgs bosons, R-parity violating SUSY couplings, leptoquarks... e p n Q-4mec2 • (A,Z)  (A,Z-2) + 2 e+ (+2e) ++ Q-2mec2 • e- + (A,Z)  (A,Z-2) + e+ (+2e )+/EC Q • 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)

  10. Advantages • Source = detector • Semiconductor (Good energy resolution, clean) • Room temperature • Modular design (Coincidences) • Two isotopes at once • Industrial development of CdTe detectors • 116Cd above 2.614 MeV • Tracking („Solid state TPC“)

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

  12. Background 116Cd (Q=2805 keV) • Alphas, Betas, Gammas • Cosmogenics Measurement: E. Porras et al., NIM B 111, 325 (1996) • neutrons 113Cd (nth,)114Cd • 2 • muon induced neutrons

  13. 2 - decay 2 is ultimate, irreducible background Energy resolution important semiconductor Fraction of 2 in 0 peak: S. Elliott, P. Vogel, Ann. Rev. Nucl. Part. Sci. 2002 Signal/Background: + Tracking option

  14. The 2x2 prototype Setup installed at Gran Sasso Underground Laboratory 4 naked 1cm3 CdZnTe more than 2.5 kg x days of data

  15. Neutrons Worry (if not enriched in 116Cd): 113Cd (nth,)114Cd MCNP simulation of the full set-up

  16. Calibration 2.4% energy resolution at 2614 keV Much better ones available A little bit of cooling helps

  17. Comparison of measurements 0.5 cm3, surface, no shielding „old“ prototype, LNGS, no shielding „old“ prototype, LNGS, shielding, no veto

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

  19. New versus old prototype

  20. Physics - 113Cd 113Cd one of only three 4-fold forbidden -emitters known in nature T1/2 = (8.2 ± 0.2 (stat.) +0.2-1.0 (sys)) 1015 yrs C. Goessling et al., nucl-ex/0508016

  21. First results H.Kiel, D. Münstermann, K. Zuber, Nucl. Phys. A 723,499 (2003) 0 COBRA Current EC-modes Current COBRA T1/2 close to 1020 years obtained Current results are preliminary

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

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

  24. The 64 detector array Aim for next 2 years: The next step towards a large scale experiment, Scalable modular design, explore coincidences Mass is factor 16 higher, about 0.5 kg CdZnTe Include: CoolingNitrogen flushing • Physics: • - Can access • 2ECEC in theoreticallypredicted region • Precision measurement of 113Cd • - New limits All detectors are at Dortmund

  25. Next steps • March - October 2005: Run prototpye with new DAQ • August - October: Perform test measurements with the new 64 detectors • October 2005: Installation of the detector provided by the Freiburg Research Centre • End of 2005: Installation of the 64 detector array at LNGS (4x4x4 cube), improvement on shielding (cooling, air-tight) • Work on shielding optimisation, active veto/signal enhancer and pixelated detectors

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

  27. Back of the envelope T1/2 = ln2 • a•NA• M • t / N (tT) ( Background free) 50 meV implies half-life measurements of 1026-27 yrs 1 event/yr you need 1026-27 source atoms This is about 1000 moles of isotope, implying 100 kg Now you only can loose: nat. abundance, efficiency, background, ...

  28. A real time low-energy solar neutrino experiment? e Threshold energy: 464 keV e e 7Be contribution g.s. alone: 227 SNU 116In  = 14s 116Cd 116Sn K. Zuber, Phys. Lett. B 571,148 (2003) Dimension it right! Current idea: 40x40x40 CdZnTe detectors = 420 kg, enriched in 116Cd

  29. The solid state TPC Introduce tracking properties by using segmented or pixellated electrodes and pulse shape analysis Single electron spectra Angular correlation coefficient 

  30. Pixellated detectors We have two 2D pixellated detectors running 3D - Pixelisation: Solid state TPC

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

  32. 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

  33. Einstein was right

  34. Join the Party!

  35. The background model Input: Pertinax (grid, base), detectors, paint and copper Currently limiting background: Passivation paint on detectors

  36. 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)

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