GERDA @ LNGS (GERmanium Detector Assembly

1
GERDA _at_ LNGS(GERmanium Detector Assembly

• Stefan Schönert
• MPIK Heidelberg
• NOW 2004, Sept. 12, 2004

2
Physics goals
Primary Objective
0??? (A,Z) ? (A,Z2) 2e-
(decay generated by (V-A) cc-interaction via
exchange of three Majorana neutrinos)
mee ?i Uei ² mi
Effective neutrino mass

• 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 Qßß 2039 keV
3
Range of mee derived from oscillation experiments
?mee f(m1, ?m²sol, ?m²atm, ?12 , ?13, ?-?)
Sensitivity of this project
F.Feruglio, A. Strumia, F. Vissani, NPB 659
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 (bgds) key to
  sensitivity
• Lifetime limit
• w/o backgrounds t1/2 ? (MT)
• with backgrounds t1/2 ? (MT)1/2
• Bgds 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 bgds 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
  lt10-3 / keV kg y
• gt15 kg y (free of background) scrutinize claim
  (97.8 excl. or 5 sigma confirmation)
• Sensitivity 31025 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 21026 y, 0.09-0.29 eV
• Phase III (depending on physics results of Phase
  III and on the understanding of backgrounds)
• world-wide collaboration 500 kg

8
External shield design
9
(No Transcript)
10
(No Transcript)
11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
Design Considerationscosmogenic Co-60 in
Ge-diodes
Qßß

• 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

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 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)

19
60Co no vs. active suppression
20
Ongoing RD programBare Ge-diode in LAr
simultaneous readout of scintillation light
Wavelength- shifter (WLS)
VM2000 Reflector/WLS foil
54Mn source (E?835 keV)
Ge crystal
Nylon fixture
r10 cm
21
Liquid Argon Germanium Test Bench (LArGe-TB)
Vol. 1.3 m3 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)