Operation of bare Ge-diodes in LN/LAr 1 st IDEA meeting Como, April 8 (2004) Stefan Schoenert

LNGS-LoI 35/04 “ A new 76 Ge Double Beta Decay Experiment at LNGS” submitted to LNGS-SC INFN LNGS, Assergi, Italy JINR, Dubna, Russia MPI für Kernphysik, Heidelberg, Germany 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 Physikalisches Institut, Univ. Tübingen, Germany Collaboration forming ongoing!

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/ (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!

The proposed new low-level LNGS: Dual purpose 1)R&D: Pioneering low-level facility to operate germanium detectors several orders of magnitude below the current state-of-the-art  major step towards ultimate Ge-76 DBD experiment in the 10 meV mass range 2)Physics: Operate germanium diodes free of backgrounds up to few 100 kg-years –to scrutinize on short time scale with high significance recent claim for evidence of 0 ββ DBD by Klapdor- Kleingrothaus’ group, –to probe Ge-76 0 ββ half life to 2 · y (m < 0.09 – 0.29 eV) if refuted

Time schedule of Phase I/II

Schedule 2004/5 Start of Construction

Tasks as proposed Work Package 7 WP-B4 Operation of Ge-diodes in Liquid N 2 Residual background components in Ge-diode-based experiments may potentially be overcome by operating the Ge crystal directly in liquid nitrogen, an ideal shielding material to protect against external gamma radiation. R&D is needed however to achieve high purity in the N 2 liquid phase. Task objectives:  Study of adsorption materials, especially for Kr and other potential contaminants like cosmogenic 7 Be.  Upgrade of the potential of the existing nitrogen (gas) purification plant (which is housed in LNGS) in order to serve a large self-shielding liquid nitrogen tank (inner diameter above 12 m)  Test operation of Ge diodes in purified nitrogen Cooperation between the overlapping working groups is foreseen with JRA1 (Task 3). TASK B4: Operation of Ge-diodes in Liquid N 2 Year 1 Year 2 Year 3 Year 4 Year 5 Study of special molecular sieves Design of a LN 2 purification plant Realization of a LN 2 purification plant Tests of Ge-diodes in purified LN 2

Milestones as proposed 7 Heidelberg (lead), Gran Sasso, UNIZAR Milest ones Definition of absorbers for nitrogen purification Tests of nitrogen purification capability completed Upgrade of the existing nitrogen (gas) purification plant to a nitrogen (liquid phase) purification plant Completion of a nitrogen purification facility Operation of Ge diodes in (purified) liquid nitrogen Delive rables Technical table with absorber materials for nitrogen purification Design of a liquid nitrogen purification plant Report on the technical aspects of the upgrade operation of the existing ntrogen purification plant Technical report on the purification capability of the realized facility Scientific papers and reports on Ge diodes operating in liquid nitrogen Year 1Year 2 Year 3 Year 4 Year 5

Planned adjustments 1)Need to accelerate project to align with schedule of proposed experiment 2) Include liquid Ar as candidate for cryogenic shielding fluid

18 months plan After 6 months:Rn/Kr measurements in LN/LAr of various qualities test of absorbers for Kr removal in LN/LAr After 12 months:design of upgraded of LTA and start of procurement After 18 months:completion of upgrade of purification system Expense plan to be worked out in detail