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