GERDA: the Germanium Detector Array at LNGS
IDEA meeting, April 14/15, Orsay
Stefan Schoenert, MPIK Heidelberg
INFN LNGS, Assergi, ItalyA.Di Vacri, M. Junker, M. Laubenstein, C. Tomei, L. Pandola
JINR Dubna, RussiaS. Belogurov,V. Brudanin, V. Egorov, K. Gusev, S. Katulina, A. Klimenko, O. Kochetov, I. Nemchenok, V. Sandukovsky, A. Smolnikov, J. Yurkowski, S. Vasiliev,
MPIK, Heidelberg, GermanyC. Bauer, O. Chkvorets, W. Hampel, G. Heusser, W. Hofmann, J. Kiko, K.T. Knöpfle, P. Peiffer, S. Schönert, J. Schreiner, B. Schwingenheuer, H. Simgen, G. Zuzel
Univ. Köln, GermanyJ. Eberth, D. Weisshaar
Jagiellonian University, Krakow, PolandM.Wojcik
Univ. di Milano Bicocca e INFN, Milano, ItalyE. Bellotti, C. Cattadori
INR, Moscow, RussiaI. Barabanov, L. Bezrukov, A. Gangapshev, V. Gurentsov, V. Kusminov, E. Yanovich
ITEP Physics, Moscow, RussiaV.P. Bolotsky, E. Demidova, I.V. Kirpichnikov, A.A. Vasenko, V.N. Kornoukhov
Kurchatov Institute, Moscow, RussiaA.M. Bakalyarov, S.T. Belyaev, M.V. Chirchenko, G.Y. Grigoriev, L.V. Inzhechik, V.I. Lebedev, A.V. Tikhomirov, S.V. Zhukov
MPP, München, GermanyI. Abt, M. Altmann, C. Büttner. A. Caldwell, R. Kotthaus, X. Liu, H.-G. Moser, R.H. Richter
Univ. di Padova e INFN, Padova, ItalyA. Bettini, E. Farnea, C. Rossi Alvarez, C.A. Ur
Univ. Tübingen, GermanyM. Bauer, H. Clement, J. Jochum, S. Scholl, K. Rottler
GERDA Collaboration
71 physicists / 12 institutions / 4 countries
GERDA @ Gran Sasso:experimental concept
• HP Ge-diodes (76Ge): point-like energy deposition at Q = 2039 keV
• Operation of bare Ge diodes in high-purity LN2 / LAr shield (Heusser, Ann, Rev. Nucl. Part. Sci. 45 (1995) 543); 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))
• Baseline: LN2; possible upgrade LAr: =1.4 g/cm3, active anti-coincidence with scintillation light from LAr
• Reduction of backgrounds key to sensitivity : – Half-life limit
• w/o backgrounds: t1/2 (MT)• with backgrounds: t1/2 (MT)1/2
Goal: background free!
Why Ge-76 ?
• High resolution (4 keV @ Q): no bgd from 2-mode
• Huge leap in sensitivity possible ……applying ultra-low background techniques…novel background / 0- signal discrimination
methods (ie. point-like vs. compton events)• Segmentation & pulse shape (with true coaxial detectors) • Liquid argon scintillation read out
• Phased approach: increment of target mass• Probably only method to scrutinize 0-DBD
claim on short time scale: test T1/2, not mee !
GERDA: Baseline design
Clean roomlock
Vacuum insulated copper vessel
Water tank / buffer/ muon veto
Liquid N/Ar
Ge Array
Phases and physics reach of GERDA
M·T
(M·T)1/2
10-3 / (keV·kg·y)
10-1 / (keV·kg·y)
Phase-IHdM & IGEX
3·1025
Phase-II+new diodes
2·1026
KK
2007 2010
Phases and Physics reach of GERDA world-wide collaboration needed for Phase-III; coop. with MAJORANA started
Phase-II
Phase-III
Phase-I
10-1/(keV·kg·y)
10-2/(keV·kg·y)
10-3/(keV·kg·y)
Phases and Physics reach of GERDA
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V
Lightest neutrino (m1) in eV
F.F
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trumia, F
. Vissani, N
PB
659
Phase I:
Phase II:
Phase III:
Backgrounds in GERDA
Source B [10-3 cts/(keV kg y)]
Ext. from 208Tl (232Th) <1
Ext. neutrons <0.05
Ext. muons <0.1
Int. 68Ge (t1/2= 270 d) 12
Int. 60Co (t1/2= 5.27 y) 2.5
222Rn in LN/LAr <0.2
208Tl, 238U in holder <1
Surface contam. <0.6
180 days exposure after enrichment + 180 days underground storage
30 days exposure after crystal growing
Assumptions:
Target for phase II: B 10-3 cts/(keV kg y) additional bgd. reduction techniques
derived from measurements and MC simulations
Background signature: example Co-60
Multi-site energy deposition inside HP-Ge diode
Co-60
Energy deposition in surrounding medium
Ideal detector:1) Measure energy in surrounding
shielding material LAr calorimeter
2) Measure locations of energy deposition inside the crystal
Segmentation
Background reduction techniques
• Anti-coincidence between detectors
• Segmentation of readout electrodes (Phase II)
• Pulse shape analysis (Phase I+II)
• Waiting (Ge-68, …)
• Coincidence in decay chain
• Scintillation light detection (LArGe)
Background reduction techniques
• Anti-coincidence between detectors
• Segmentation of readout electrodes (Phase II)
• Pulse shape analysis (Phase I+II)
• Waiting (Ge-68, …)
• Coincidence in decay chain
• Scintillation light detection (LArGe)
2: 1.332 MeV: Emax = 318 keV
1: 1.173 MeV
• T0 : crystal growing• 0.017 Bq/kg per day exposure• Test: detector production in 7.4 days • Assume 30 days 2.5 ·10-3 / (keV·kg·y)• HdM: ~5·10-3 / (keV·kg·y) in 2006
• T0 : crystal growing• 0.017 Bq/kg per day exposure• Test: detector production in 7.4 days • Assume 30 days 2.5 ·10-3 / (keV·kg·y)• HdM: ~5·10-3 / (keV·kg·y) in 2006
Example 60Co
60Co: segmentation and LAr Ge-anticoinc.
~1000
Liquid Argon
Nseg = 1AND
LAr anticoinc
Q
2 kg
MC simulation
LAr Ge-anticoincidence
Liquid Argon
20 cm
MC Simulation
Suppression factor limitedby escape events!
~5
LAr Ge-anticoincidence
Liquid Argon
100 cm
MC Simulation
~60
Suppression factor limitedby dead layer0.18 kg
Status of GERDA• March 2004: LoI to LNGS
• Sep. 2004: Proposal to LNGS
• Sep. 2004: 70% of funding secured
• Feb. 05: Approval by LNGS
• Feb. 05: Ge-76 enrichment for Phase II started at ECP
• Feb. 05: Underground locations frozen (in front of LVD, TIR tunnel Sec. A-B & adjacent to LUNA II)
• March 05: LArGe facility (i.e. detector laboratory Phase I) under construction
• March 05: Technical proposal (Vers. 0.1)
• Autumn 06 (Goal): Detector filling and commissioning
Infrastructures in Hall A: Super-insulated cryogenic vessel
Cu-cryostat:hanging from neck
Cu-cryostat:resting on pads
Steel-cryostat:with optimized shielding
Two design studies for Cu-cryostat available:
•Cu-cryostat purchase process commenced with publication in ’Supplememnt of the Official Journal of the European Union’ a ’Prior Information Notice’ - SIMAP-MPI-K 31 Jan’05 ID:2005-002331; 7 companies expressed interest
•Decision taking Cu vs. steel cryostat: Cu-Steel welding tests and certification
LArGe Facility
•Barrack modification close to completion
•Re-machined shielding system of LArGe underground
Underground detector laboratory
Testing and modification of enriched detectors
November, 2004, in LENS barrack(prior to barrack refurbishment)
ANG1 ANG2 ANG3 ANG4 ANG5
HdMo
Setup
3.0 3.4 3.0 3.5 3.4
GERDA
Lab, Jan.05
3.9 2.7 3.0 2.8 3.1
Notes Warm Up
PA gain
‘jumps’
•Co-60 source - absolute efficiency (done)•Ba-133 source - dead layer thickness estimation (done)•Check of ANG2 (ongoing)
Energy resolution at 2.615 MeV
Modification of enriched detectors
Design study for a Cu/Si/PTFE-onlydetector support/contact system
Alternative: Silicon support
Minimizing mass vs. strength(current design: factor 5 safety)
New detectors for Phase II:Procurement of enriched Ge
• Ge procurement is done in two steps:
1) procurement of 15 kg of natural Ge (‘test run’)
2) subsequently procurement of 30-35 kg of 76Ge (‘real run’)
• Both samples produced in Siberia / Russian Federation
• 15 kg ‘test run’ (6N) Ge shipped in same way as enriched sample.
• Specially designed protective steel container (PSC) which reduces activation by cosmic rays by factor 20 is used for transportation
Procurement of natural Ge successfully concluded; sample received at MPI Munich on March 7, 2005
New detectors for Phase II
• Production of 30-35 kg sample of enriched Ge-76 started in Siberia in February, 2005;
• Production time: 6 months • Increase of purity of enriched Ge-76 to 99.99 %
(99.8% originally quoted)• R&D on chemical purification technique: yield
≥85%, to be compared to the 70% of the standard procedure
• Segmented prototype detectors (p-type) ordered and are currently being produced
Summary/Outlook
• GERDA collaboration operational; plans to further grow (Phase II and beyond)
• Major progress achieved over last 6 months• Co-operation with Majorana (MaGe, LArGe) very
positive: mutual benefit!• Schedule: items on critical path:
– Funding for water tank and muon veto (water Cherenkov)
– Integration of cryo-vessel, water tank, super-structure, laboratory building and penthouse
• GERDA well on its way