Transcript GERDA @ LNGS (GERmanium Detector Assembly

GERDA @ LNGS
(GERmanium Detector Assembly
Stefan Schönert
MPIK Heidelberg
NOW 2004, Sept. 12, 2004
Physics goals
Primary Objective:
u
d
0: (A,Z)  (A,Z+2) +
2e-
W- e
W-
d
u
Effective neutrino mass:
e-
mee = |i Uei ² mi |
e
L=2
e-
(decay generated by
(V-A) cc-interaction
via exchange of
three Majorana
neutrinos)
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
Range of mee derived from
oscillation experiments
mee = f(m1, m²sol, m²atm, 12 , 13, -)
Phase II:
| mee| in eV
Sensitivity
of this
project:
I:
F.Feruglio, A. Strumia, F. Vissani, NPB 659
H.V. Klapdor-Kleingrothaus, A. Dietz, O.
Chkvorets, I.V. Krivosheina, NIM A,
2004
Phase
Phase III:
Lightest neutrino (m1) in eV
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:
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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
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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:
• with backgrounds:
t1/2  (MT)
t1/2  (MT)1/2
 Goal: background free!
• 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
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
Design Considerations:
cosmogenic Co-60 in Ge-diodes
1
2
Qββ
β
2+β
1+ 2+β
•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
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
,
Wavelength shifter Reflector (VM2000)
Reduction factor ~100
Ongoing R&D program
No. of counts
Bare Ge-diode in LAr: simultaneous readout of scintillation light
Mounting
thecrystal
PMTrun
Opening cryostat
after
first
germanium
Wavelengthshifter (WLS)
No anticoincidence
LAr-anticoinc. (r=10 cm)
VM2000
Reflector/WLS
foil
Channel
54Mn
source
(E=835 keV)
Ge crystal
Nylon fixture
r=10 cm
No anticoincidence
LAr-anticoinc. (r=10 cm)
Liquid Argon Germanium Test
Bench (LArGe-TB)
Vol. 1.3 m3
Height 3.6 m
Diam. 2.5 m
Refurbish of
LENS 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)