GERDA @ LNGS(GERmanium Detector Assembly

Stefan Schönert

MPIK Heidelberg

NOW 2004, Sept. 12, 2004

Physics goals

0: (A,Z) (A,Z+2) + 2e-

d

d

u

u

e-

e-

W-

W- e

e

L=2

Primary Objective:

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

mee = |i Uei ² mi |(decay generated by (V-A) cc-interaction via exchange of three Majorana neutrinos)

Effective neutrino mass:

Range of mee derived from oscillation experimentsmee = f(m1, m²sol, m²atm, 12 , 13, -)

| m

ee|

in e

V

Lightest neutrino (m1) in eV

F.F

eruglio, A. S

trumia, F

. Vissani, N

PB

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:

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]

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

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!

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

External shield design

•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

Design Considerations:cosmogenic Co-60 in Ge-diodes

β

1 2

2+β1+2+β

Qββ

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)

Bgd. summary (Phase II)

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)

60Co: no vs. active suppression

,

Reflector (VM2000)Wavelength shifter

Reduction factor ~100

Ongoing R&D programBare Ge-diode in LAr: simultaneous readout of scintillation light

r=10 cm

VM2000Reflector/WLSfoil

Wavelength-shifter (WLS)

54Mn source(E=835 keV)

Ge crystal

Nylon fixture

germanium crystalMounting the PMTOpening cryostat after first run

LAr-anticoinc. (r=10 cm)

No anticoincidence

No anticoincidence

LAr-anticoinc. (r=10 cm)

No

. of

cou

nts

Channel

Liquid Argon Germanium Test Bench (LArGe-TB)

Vol. 1.3 m3

Height 3.6 mDiam. 2.5 m

Refurbish ofLENS LBF

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)