Operation of bare Ge-diodes in LN/LAr

1st IDEA meeting

Como, April 8 (2004)

Stefan Schoenert

LNGS-LoI 35/04 “A new 76Ge 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: 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!

The proposed new low-level facility @ 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 0ββ DBD by Klapdor-Kleingrothaus’ group,

– to probe Ge-76 0ββ half life to 2·1026 y (m < 0.09 – 0.29 eV) if refuted

Time schedule of Phase I/II

Sch

edul

e 20

04/5

Start of Construction

Tasks as proposed

Work Package 7WP-B4

Operation of Ge-diodes in Liquid N2

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 N2 liquid phase.

Task objectives:Study of adsorption materials, especially for Kr and other potential contaminants like cosmogenic 7Be. 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 nitrogenCooperation between the overlapping working groups is foreseen with JRA1 (Task 3).

TASK B4: Operation of Ge-diodes in Liquid N2

Year 1 Year 2 Year 3 Year 4 Year 5

Study of special molecular sieves

Design of a LN2 purification plant

Realization of a LN2 purification plant

Tests of Ge-diodes in purified LN2

Milestones as proposed

7

Heidelberg (lead), Gran Sasso, UNIZAR

Milestones

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

Deliverables

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 1 Year 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 qualitiestest 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