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GERDA @ LNGS (GERmanium Detector Assembly Stefan Schönert MPIK Heidelberg NOW 2004, Sept. 12, 2004
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Physics goals 0 :(A,Z) (A,Z+2) + 2e - d d u u e-e- e-e- W-W- W-W- e e L=2 Primary Objective: Majorana nature, Mass scale, Majorana CP phases Method: Operation of HP Ge-diodes enriched in 76 Ge in (optional active) cryogenic fluid shield. Line search at Q ββ = 2039 keV m ee = | i U ei ² m i | (decay generated by (V-A) cc-interaction via exchange of three Majorana neutrinos) Effective neutrino mass:
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Range of m ee derived from oscillation experiments m ee = f(m 1, m² sol, m² atm, 12, 13, - ) | m ee | in eV Lightest neutrino (m 1 ) in eV F.Feruglio, A. Strumia, F. Vissani, NPB 659 H.V. Klapdor-Kleingrothaus, A. Dietz, O. Chkvorets, I.V. Krivosheina, NIM A, 2004 Sensitivity of this project: Phase I: Phase II: Phase III:
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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]
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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
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The experimental concept Reduction of backgrounds (bgd’s) key to sensitivity : –Lifetime limit w/o backgrounds: t 1/2 (MT) with backgrounds: t 1/2 (MT) 1/2 Bgd’s in HdM & IGEX dominated by external activities in the shielding and cladding materials Operation of bare Ge diodes in LN 2 / 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!
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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 · 10 25 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 · 10 26 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
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External shield design
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T 0 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 Design Considerations: cosmogenic Co-60 in Ge-diodes β 11 22 2+β2+β 1+1+ 2+β2+β Q ββ
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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)
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Bgd. summary (Phase II)
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LAr scintillation readout: example 60 Co Cosmogenic activities: Production after completion of crystal growth Exposure to cosmic rays above ground for 10 days: 0.9 ·10 -3 /(kg keV y)
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60 Co: no vs. active suppression ,, Reflector (VM2000) Wavelength shifter Reduction factor ~100
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Ongoing R&D program Bare Ge-diode in LAr: simultaneous readout of scintillation light r=10 cm VM2000 Reflector/WLS foil Wavelength- shifter (WLS) 54 Mn source (E =835 keV) Ge crystal Nylon fixture germanium crystal Mounting the PMT Opening cryostat after first run LAr-anticoinc. (r=10 cm) No anticoincidence LAr-anticoinc. (r=10 cm) No. of counts Channel
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Liquid Argon Germanium Test Bench (LArGe-TB) Vol. 1.3 m 3 Height 3.6 m Diam. 2.5 m Refurbish of LENS LBF
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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)
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