The Germanium Detector Array for the search of neutrinoless
decays of 76Ge at LNGS(GERDA) LNGS, ITALY
Stefan Schoenert, MPIK HeidelbergInternational School of Nuclear Physics
27th courseNeutrinos in Cosmology, in Astro-, Particle and Nuclear Physics
INFN LNGS, Assergi, ItalyA.Di Vacri, M. Junker, M. Laubenstein, C. Tomei, L. Pandola
JINR Dubna, RussiaV. 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
IMMR, Geel, BelgiumM. Hult
INR, Moscow, RussiaI. Barabanov, L. Bezrukov, A. Gangapshev, V. Gurentsov, V. Kusminov, E. Yanovich
ITEP Physics, Moscow, RussiaS. Belogurov, V.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, K. Kroeninger, X. Liu, B. Majorovits, 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
Physics goals of GERDA
0: (A,Z) (A,Z+2) + 2e-
d
d
u
u
e-
e-
W-
W- e
e
L=2
Primary Objective:
Effective mass:
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 light Majorana neutrinos)
Other Physics: WIMP DM search
Majorana nature
= G(Q,Z) |Mnucl|2 mee2,
GERDA @ Gran Sasso:experimental concept
• HP Ge-diodes (86%76Ge): point-like energy deposition at Q = 2039 keV
• Operation of bare Ge diodes in high-purity LN2 or 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 within planned exposure”!
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
~20 kg
3·1025 (90 % CL)
Phase-IIHdM & IGEX +new diodes
~40 kg
2·1026 (90 % CL)<mee> < 0.09 – 0.29 eV
KK
2008 2010
Phases and Physics reach of GERDA world-wide collaboration 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) 6·1027
Phases and Physics reach of GERDA
| m
ee|
in e
V
Lightest neutrino (m1) in eV
F.F
eruglio, A. S
trumia, F
. Vissani, N
PB
659
Phase I:
Phase II:
Phase III:
…how to reach <10-3/(keV·kg·y)?
Borexino Collab. PLB 563 (2003)
10-3/(keV·kg·y)
Q
BOREXINO Counting Test Facility (CTF)(‘world record’)
Liquid scintillator target
BOREXINO ~10-5/(keV·kg·y)
External background: graded shielding Activity of Tl-208 (Bq/kg)
Rock/concrete 3 ·106
Cu (NOSV/OFO1),Pb <20Water <5LN, Ar ~0
GERDA: Baseline design
Clean roomlock
Vacuum insulated copper vessel
Water tank / buffer/ muon veto
Liquid N/Ar
Ge Array
Under discussion: ‘third wall’
copper cryogenic vessel
Detector support & contacts
Cu: 81 gPTFE: 6.4 gSi: 4.2 g
MC: <2 ·10-3 (keV kg y) -1
Phase I: HdM & IGEX (p-type coaxial)
PrototypeSpring
Phase II:•true-coaxial •3x6 segmented•n-type Ge diode
Support: ~ 40 g
New detectors for Phase II:Procurement of enriched Ge
natGe sample received March 7, 2005
1) procurement of 15 kg of natural Ge (‘test run’)
2) enrichment of 37.5 kg of Ge-76 completed !
Specially designed protective steel container reduces activation by cosmic rays by factor 20
Backgrounds in GERDA
Source B [10-3 cts/(keV kg y)]
Ext. from 208Tl (232Th) <1
Ext. neutrons <0.05
Ext. muons (veto) <0.03
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
phase I : B 10-2 cts/(keV kg y)phase II: B 10-3 cts/(keV kg y) additional bgd. reduction
derived from measurements and MC simulations
Muon veto
Background reduction techniques
• Muon Veto
• Anti-coincidence between detectors
• Segmentation of readout electrodes (Phase II)
• Pulse shape analysis (Phase I+II)
• Coincidence in decay chain (Ge-68)
• Scintillation light detection (LArGe)
Background reduction techniques
• Muon veto
• Anti-coincidence between detectors
• Segmentation of readout electrodes (Phase II)
• Pulse shape analysis (Phase I+II)
• Coincidence in decay chain (Ge-68)
• Scintillation light detection (LArGe)
K. Kroeniger
Background simulations with MaGe
(common Majorana–Gerda Geant4 MC framework)
Description of the Gerda setup including shielding
(water tank, Cu tank, liquid Nitrogen), crystals array and
kapton cables
top -vetowater tank
lead shieldingcryo
vessel
neck
Ge array
MaGe simulation of muon induced backgrounds
Flux at Gran Sasso: 1.1 /m2 h (270 GeV)
Input energy spectru
m
from Lipari and Stanev, Phys.
Rev. D 44 (1991) 3543
Energy (keV)
Input angular spectru
m
cos
Teramo side
MaGe: cosmic ray muons – Ge signalPhase I: 9 Ge crystals for a total mass of 19 kg; threshold: 50 keV
Energy (MeV)
5.5 yearsSum spectrum without and with anticoincidence
Energy (MeV)
(1.5 2.5 MeV): 3.3·10-3 counts/keV kg y
annihilation peak
(~4·10-3 counts/keV kg y in H-M simul.) C. Doerr, NIM A 513 (2003) 596
1.5 MeV 2.5 MeVanticoincidence between 9 crystals reduces background index by factor 3
1.0 · 10-3 cts/keV kg y
MaGe: cosmic ray muons - muon veto
Energy (MeV)Threshold 120 MeV all events cut but two 120MeV in water (~60 cm) 30,000 ph. 40 p.e. (0.5% coverage) 80-90 PMTs
Energy deposition in water Cherenkov detector in coincidence with Ge detectors (Ethr>50 keV)
5.5 years
No cuts 3.3 · 10-3 (cts/keV kg y)
Ge anti-coincidence 1.0 · 10-3
Ge anti-coinc.+ Top -veto (plastic scint.) 4.4 · 10-4
Cerenkov -veto < 3 · 10-5 (95% CL)
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)
• 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)
Internal backgrounds: example 60Co
2 kg
60Co background spectrum
1 2
1+ 2
Q
MC simulation
2 kg
60Co: suppression by segmentation
QMC simulation
2 kg
60Co: suppression by segmentation
~10 (7 seg.)Nseg = 1
QMC simulation
Nhit = 3
illustration: Simple 7-fold segmentation
MaGe: 60Co suppression by segmentation and anti-coincidence
6-3z segmentation;Prototype under construction
N crystals = 1
N segments = 1
Number of crystals
Number of segments
probability per decay to deposit energy within Q ROI per 1 keV energy bin after combined cuts:(18-fold segm.)
P = 4.7·10-6/keV
(factor ~35 reduction w/rto single unseg. detector)
60Co: suppression by LAr Ge-anticoinc.
~100LAr anticoinc.
Liquid Argon
QMC simulation
2 kg
60Co: segmentation and LAr Ge-anticoinc. are orthogonal suppression methods
~1000
Liquid Argon
Nseg = 1AND
LAr anticoinc
Q
2 kg
MC simulation
Experiment: LAr Ge-anticoincidence
54Mn-source
Liquid Argon
20 cm
0.18 kg
Experiment: LAr Ge-anticoincidence
Liquid Argon
20 cm
Experimental Data
~5
0.18 kg
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
90 cm
Status - Outlook2004
• Feb Letter of Intent to LNGS, hep-ex/0404039• Sep formation of collaboration• Oct funding requests approved by MPG• Oct Proposal to LNGS, www.mpi-hd.mpg.de/GERDA/proposal.pdf
2005• Jan `prior information notice’ about cryostat tendering in SIMAP• Feb GERDA approved by LNGS, location in Hall A in front of LVD• Mar Technical Proposal to LNGS, 30 kg of enriched Ge-76 ordered• May funding requests approved by INFN• Jun funding request approved by BMBF• Jul Ge-76 order enlarged to 37.5 kg• Jul FMECA & HAZOP safety study for cryostat submitted to LNGS(‘safe if designed & fabricated according to the rules’)• Sep safety iteration with LNGS: “ALARP - third wall?”• subsequently: tendering for water tank, first orders for cryostat
2006• Summer start of construction of water tank in Hall A• ... installation of cryostat, clean room & lock, μ veto, lab rooms
2007• commissioning, start of physics run
Summary
• approved by LNGS with location in Hall A,
• substantially funded by BMBF, INFN, MPG, and Russia in kind
• construction to start in LNGS Hall A in summer 2006
• parallel and fast R&D for phase II
• start of data taking in 2007
goal: phase I : background 0.01 cts / (kg٠keV٠y)
► scrutinize KKDC result within 1 year
phase II : background 0.001 cts / (kg٠keV٠y)
► T1/2 > 2٠1026 y , <mee> < 0.09 – 0.29 eV
phase III : world wide collaboration
► T1/2 > ~1028 y , <mee> ~10 meV