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GERDA @ LNGS (GERmanium Detector Assembly

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  1. GERDA @ LNGS(GERmanium Detector Assembly Stefan Schönert MPIK Heidelberg NOW 2004, Sept. 12, 2004

  2. u e- d ne L=2 W- ne W- d e- u Physics goals Primary Objective: 0: (A,Z)  (A,Z+2) + 2e- (decay generated by (V-A) cc-interaction via exchange of three Majorana neutrinos) mee= |iUei ²mi | Effective neutrino mass: • Majorana nature, Mass scale, Majorana CP phases Method: Operation of HP Ge-diodes enriched in 76Ge in (optional active) cryogenic fluid shield. Line search at Qββ= 2039 keV

  3. H.V. Klapdor-Kleingrothaus, A. Dietz, O. Chkvorets, I.V. Krivosheina, NIM A, 2004 | mee| in eV Phase I: Lightest neutrino (m1) in eV Phase II: Phase III: Range of meederivedfrom oscillation experiments mee= f(m1, m²sol, m²atm, 12 , 13, -) Sensitivity of this project: F.Feruglio, A. Strumia, F. Vissani, NPB 659

  4. Status of GERDA • Proto-collaboration formed in Feb. 2004 • LoI discussed at LNGS April 2004 • Formal collaboration forming completed Sep. 9/10 (incl. MoU, etc.) • Proposal submission to LNGS SC Sep. 17 • Discussion with LNGS SC Oct. 14-16 • Funding: • Kurchatov, INR, ITEP (in-kind contribution of Ge-76 diodes) • MPG (MPIK Heidelberg + MPI Munich) [approved] • INFN (LNGS, Milano, Padova) [discussion Sep. 04] • BMBF (Tuebingen) [call for proposal issued]

  5. Collaboration • INFN LNGS, Assergi, Italy • JINR, Dubna, Russia • MPI für Kernphysik, Heidelberg, Germany • Univ. Cracow, Poland • Institut für Kernphysik, Univ. Köln, Germany • Univ. di Milano Bicocca e INFN Milano, Milano, Italy • INR, Moscow, Russia • ITEP, Moscow, Russia • Kurchatov Institute, Moscow, Russia • MPI für Physik, München, Germany • INFN and Univ., Padova, Italy • Physikalisches Institut, Univ. Tübingen, Germany

  6. The experimental concept • Reduction of backgrounds (bgd’s) key to sensitivity : • Lifetime limit • w/o backgrounds: t1/2  (MT) • with backgrounds: t1/2  (MT)1/2 • Bgd’s in HdM & IGEX dominated by external activities in the shielding and cladding materials • Operation of bare Ge diodes in LN2 / LAr shield (Heusser, Ann, Rev. Nucl. Part. Sci. 45 (1995) 543); other proposals based on this idea: GENIUS (H.V. Klapdor-Kleingrothaus et. al., hep-ph/9910205 (1999)); GEM (Y.G. Zdesenko et al., J. Phys. G27 (2001)) • Shielding against external bgd’s by high-purity cryogenic fluid shield. Optional: active anticoincidence with scintillation light from LAr  Goal: background free!

  7. Phases of the experiment and physics reach • Phase I: implementation of existing Ge-76 diodes (~20 kg) of HdM and IGEX in new experiment (“background free”) • operation in LN2/LAr with external background <10-3 / keV kg y • >15 kg y (free of background): scrutinize claim (97.8% excl. or 5 sigma confirmation) • Sensitivity: 3·1025 y, 0.24-0.77 eV • Phase II: enlarge to ~35-40 kg (segmented detectors, possibly LAr scintillation readout ) • within 2-3 years: ~100 kg y • Sensitivity: 2·1026 y, 0.09-0.29 eV • Phase III: (depending on physics results of Phase I+II and on the understanding of backgrounds) • world-wide collaboration: ~500 kg

  8. External shield design

  9. 1 2 β 2+β 2+β 1+ Design Considerations:cosmogenic Co-60 in Ge-diodes Qββ • T0 for cosmic ray exposure: completion of mono-zone refinement • Exposure to cosmic rays above ground for 10 days: 0.17 Bq/kg [Avignone 92] • 0.9 10-3 / keV kg y • Kurchatov crystals: ~5 10-3 / (keV kg y) in 2006

  10. Background discrimination techniques • Anti-coincidence between different detectors in the setup • Pulse shape analysis (PSA) • Coincidences in the decay chain (Ge-68) • Segmentation of one of the readout electrodes • Scintillation light detection (LAr)

  11. Bgd. summary (Phase II)

  12. LAr scintillation readout: example 60Co • Cosmogenic activities: • Production after completion of crystal growth • Exposure to cosmic rays above ground for 10 days: 0.9 ·10-3 /(kg keV y)

  13. , Wavelength shifter Reflector (VM2000) Reduction factor ~100 60Co: no vs. active suppression

  14. Mounting the PMT Opening cryostat after first run germanium crystal No. of counts No anticoincidence LAr-anticoinc. (r=10 cm) Channel No anticoincidence LAr-anticoinc. (r=10 cm) Ongoing R&D programBare Ge-diode in LAr: simultaneous readout of scintillation light Wavelength- shifter (WLS) VM2000 Reflector/WLS foil 54Mn source (E=835 keV) Ge crystal Nylon fixture r=10 cm

  15. Liquid Argon Germanium Test Bench (LArGe-TB) Vol. 1.3 m3 Height 3.6 m Diam. 2.5 m Refurbish of LENS LBF

  16. Schedule(provided approval, funding + LNGS refurbishments completed timely) • Start construction of infrastructure in 2005 • Detector commissioning and start physics data taking (Phase-I) 2006 • Procurement of new enriched material 2004/5 • Start of Phase-II could start early and overlap with Phase-I (funding permitted)