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

2. 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:

3. 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:

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: 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!

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 · 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

8. External shield design

15. 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 11 22 2+β2+β 1+1+ 2+β2+β Q ββ

16. 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)

17. Bgd. summary (Phase II)

18. 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)

19. 60 Co: no vs. active suppression ,, Reflector (VM2000) Wavelength shifter Reduction factor ~100

20. 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

21. Liquid Argon Germanium Test Bench (LArGe-TB) Vol. 1.3 m 3 Height 3.6 m Diam. 2.5 m Refurbish of LENS LBF

22. 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)