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GERDA: GERmanium Detector Array Searching for 0 2 decay

GERDA: GERmanium Detector Array Searching for 0 2 decay. Xiang Liu Max-Planck-Institut f ü r Physik. 0 2 introduction GERDA setup & detectors 3. Low background & high sensitivity R&D Conclusion. SNOW 2006, May 2-6 th , 2006. 2 2 decay: (A,Z)  (A,Z+2) +2e+ 2 

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GERDA: GERmanium Detector Array Searching for 0 2 decay

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  1. GERDA: GERmanium Detector Array Searching for 02 decay Xiang Liu Max-Planck-Institut für Physik • 02 introduction • GERDA setup • & detectors • 3. Low background • & high sensitivity • R&D • Conclusion SNOW 2006, May 2-6th, 2006

  2. 22 decay: (A,Z)  (A,Z+2) +2e+ 2 allowed by SM & exists. • 02 decay: (A,Z)  (A,Z+2) +2e if s Majorana & have mass. L=2 • Many isotopes can be used to search for 02. • Best limit from Heidelberg-Moscow experiment (HdMo) with 76Ge. Neutrino mixing & 02 decay Open questions: • Absolute mass scale? • Normal hierarchy or inversed? • Nature: Dirac or Majorana?  02 decay might address all. SNOW2006 Page 2

  3. Search 02 & measure T1/2 Phase I Phase II m (eV) Lightest neutrino mass (eV) G0: phase space integral M0: nuclear matrix element <m>=  Vei2 mi (Vei: neutrino mixing matrix) GERDA Phase I: Existing detectors Phase II: new detectors Future: 1 ton experiment Effective Majorana neutrino mass: m SNOW2006 Page 3

  4. GERDA new features: • Ge detectors directly submerged in LN2/LAr (as cooling & shielding) • Segmented Ge detectors (phase-II) Ge detector array LN2/LAr cryostat Water tank GERDA Setup • 02 rare process • Large amount of target mass • High efficiency detecting signal • Low background 76Ge 8% in nature,need enrichment (reduce bg) Detector = source, >95% signal effi. Excellent  (FWHM ~2 keV at 1.3 MeV), high Q value (2.04 MeV) existing detectors & experiences from HdMo & IGEX. LNGS Hall A (3800 m.w.e.) Clean room & Lock Scintillator veto (top of clean room) Čerenkov veto (PMTs in water tank) SNOW2006 Page 4

  5. (Phase II) readout cable holder HV cable suspension strings Detectors & supports Materials near detectors: as little as possible, as pure as possible. Phase-I: HdMo & IGEX detectors, sum ~15kg, non-segmented Phase-II:New detectors, sum ~25kg, 18 segments (3z6) SNOW2006 Page 5

  6. Status of Existing Phase-I Detectors • IGEX detectors testedinside Vacuum storage Can. FWHM 2.2 - 2.3keV at 1332keV • HdMo detectors stored at LNGS, all tested. • One HdMo detector taken out from Vacuum Can for testing. HdMo Setup ANG1 Ge crystal HdMo claim Signal: 28.75  6.86 events Bg level: 0.11 cts/[keV kg year] If claim true, Phase-I will have Signal: ~13 events Bg level: <0.01 cts/[keV kg year] <3 events in 10keV window at Q value. SNOW2006 Page 6

  7. Status of Phase-II Detectors • 37.5kg Ge, 87.25% 76Ge, purity >99.9% (in GeO2) enriched in Russia, transported to MPI Munich on April 3rd 2006, now stored underground (200m.w.e) • Next steps: purification, crystal pulling & detector fabrication. SNOW2006 Page 2

  8. High sensitivity = Low background a) b) Phase II Phase I a) Assessment of uncertainties in QRPA 02-decay nuclear matrix elements V.A. Rodin, A. Faessler, F. Simkovic, P. Vogel [Nucl-th 0503063] b) Search for Neutrinoless Double Beta Decay with Enriched 76Ge in Gran Sasso 1990-2003, H.V. Klapdor-Kleingrothaus, I.V. Krivosheina, A. Dietz and O. Chkvorets, Phys. Lett. B586 (2004) 198-212 SNOW2006 Page 8

  9. Use segments to reject background 02 signal: 2 electrons deposit energy very localized (<1mm) Background : Mostly Compton scattering 2~3 cm mean free path (mostly multi-segment) SNOW2006 Page 9

  10. MC simulation of bg. Water tank • MC package (MaGe) for both Gerda & Majorana. • Upper limit on contamination levels for all materials calculated. • Bg. Index calculated with available materials. Cryo vessel (Phase II) SNOW2006 Page 10

  11. 6-segment p-type detector in LN2. Co60 R&D: Ge detector properties Several test facilities being built with detectors directly in LN2/LAr. • Both n & p-type Ge cycled multi times in LN2 & LAr Similar behavior in LN2/LAr. No deterioration of performance. • One 18-segment n-type detector is under study. SNOW2006 Page 11

  12. Conclusion • Open questions in  : absolute mass? hierarchy? Majorana or Dirac? • 02might answer all these questions. • GERDA searches for 02decay in 76Ge. • Ge detectors are submerged directly in LN2/LAr (cooling & shielding). • IGEX & HdMo detectors for Phase-I. • Segmented Ge detectors for Phase-II. • Goal for bg. rate: 10-3 cts/[keV kg year] (Phase-II), difficult but feasible. • With this bg. rate, sensitivity of 0.2eV on m expected. • Several test facilities for GERDA are being built. • Both n- & p-type detectors cycled in LN2/LAr without obvious deterioration. • Once the GERDA concept is proven, global experiment with 1t Ge might be pursued (MoU with Majorana exists). SNOW2006 Page 12

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