1. The Germanium Detector Array for the search of neutrinoless  decays of 76Ge at LNGS (GERDA)
LNGS, ITALY
Stefan Schoenert, MPIK Heidelberg
International School of Nuclear Physics
27th course
Neutrinos in Cosmology, in Astro-, Particle and Nuclear Physics

2. GERDA Collaboration Univ. Tübingen, Germany INFN LNGS, Assergi, Italy
A.Di Vacri, M. Junker, M. Laubenstein, C. Tomei, L. Pandola
JINR Dubna, Russia
V. Brudanin, V. Egorov, K. Gusev, S. Katulina, A. Klimenko, O. Kochetov, I. Nemchenok, V. Sandukovsky, A. Smolnikov, J. Yurkowski, S. Vasiliev,
MPIK, Heidelberg, Germany
C. 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, Germany
J. Eberth, D. Weisshaar
Jagiellonian University, Krakow, Poland
M.Wojcik
Univ. di Milano Bicocca e INFN, Milano, Italy
E. Bellotti, C. Cattadori
IMMR, Geel, Belgium
M. Hult
INR, Moscow, Russia
I. Barabanov, L. Bezrukov, A. Gangapshev, V. Gurentsov, V. Kusminov, E. Yanovich
ITEP Physics, Moscow, Russia
S. Belogurov, V.P. Bolotsky, E. Demidova, I.V. Kirpichnikov, A.A. Vasenko, V.N. Kornoukhov
Kurchatov Institute, Moscow, Russia
A.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, Germany
I. 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, Italy
A. Bettini, E. Farnea, C. Rossi Alvarez, C.A. Ur
Univ. Tübingen, Germany
M. Bauer, H. Clement, J. Jochum, S. Scholl, K. Rottler
Russian groups own HdM and IGEX crystals: ~ 20 kg

3. Physics goals of GERDA L=2 Primary Objective:u e- W- ne
L=2
0: (A,Z)  (A,Z+2) + 2e-
Majorana nature
Effective mass:
1/t = G(Q,Z) |Mnucl|2 mee2,
(decay generated by (V-A) cc-interaction via exchange of light Majorana neutrinos)
mee = |i Uei ² mi |
Other Physics: WIMP DM search
Method:
Operation of HP Ge-diodes enriched in 76Ge in (optional active) cryogenic fluid shield.
Line search at Qββ = 2039 keV

4. 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/ (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
Bgd’s in HdM & IGEX dominated by external activities in the shielding and cladding materials
Goal: “background free within planned exposure”!

5. Phases and physics reach of GERDA
10-3 / (keV·kg·y)
2·1026 (90 % CL)
<mee> < 0.09 – 0.29 eV
 M·T
10-1 / (keV·kg·y)
 (M·T)1/2
3·1025 (90 % CL) KK
Phase-I
HdM & IGEX
~20 kg
Phase-II
HdM & IGEX
+new diodes
~40 kg
2008
2010

6. Phases and Physics reach of GERDA world-wide collaboration for Phase-III; coop. with MAJORANA started
6·1027
10-3/(keV·kg·y)
Phase-III
10-2/(keV·kg·y)
10-1/(keV·kg·y)
Phase-II
Phase-I

7. Phases and Physics reach of GERDA
| mee| in eV
Lightest neutrino (m1) in eV
Phase I:
Phase II:
Phase III:
F.Feruglio, A. Strumia, F. Vissani, NPB 659

8. …how to reach <10-3/(keV·kg·y)?
BOREXINO Counting Test Facility (CTF)
(‘world record’)
10-3/(keV·kg·y)
Q
Liquid scintillator target
BOREXINO ~10-5/(keV·kg·y)
Borexino Collab. PLB 563 (2003)

9. External background: graded shielding
Activity of Tl (Bq/kg)
Rock/concrete 3 ·106
Cu (NOSV/OFO1),Pb <20
Water <5
LN, Ar ~0

10. GERDA: Baseline design
Clean room
lock
Water tank / buffer/ muon veto
Vacuum insulated
copper vessel
Liquid N/Ar
Ge Array
Under discussion:
‘third wall’

11. copper cryogenic vessel

12. Detector support & contacts
Phase I:
HdM & IGEX (p-type coaxial)
Phase II:
true-coaxial
3x6 segmented
n-type Ge diode
Prototype
Spring
Cu: 81 g
PTFE: 6.4 g
Si: 4.2 g
MC: <2 ·10-3 (keV kg y) -1
Support: ~ 40 g

13. New detectors for Phase II: Procurement of enriched Ge
procurement of 15 kg of natural Ge (‘test run’)
enrichment of 37.5 kg of Ge-76 completed !
Specially designed protective steel container reduces activation by cosmic rays by factor 20
natGe sample received March 7, 2005

14. Backgrounds in GERDA phase I : B  10-2 cts/(keV kg y)
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
Surface contam.
<0.6
Muon veto
180 days exposure after enrichment days underground storage
30 days exposure after crystal growing
derived from measurements and MC simulations
phase I : B  10-2 cts/(keV kg y)
phase II: B  10-3 cts/(keV kg y)  additional bgd. reduction

15. 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)

16. 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

17. Background simulations with MaGe
(common Majorana–Gerda Geant4 MC framework)
top m-veto
water tank
neck
lead shielding
cryo vessel
Description of the Gerda setup including shielding (water tank, Cu tank, liquid Nitrogen), crystals array and kapton cables
Ge array

18. MaGe simulation of muon induced backgrounds
from Lipari and Stanev, Phys. Rev. D 44 (1991) 3543
Input angular spectrum
Input energy spectrum
Teramo side
Energy (keV)
cosq
Flux at Gran Sasso: /m2 h (270 GeV)

19. MaGe: cosmic ray muons – Ge signal
Phase I: 9 Ge crystals for a total mass of 19 kg; threshold: 50 keV
annihilation peak
Sum spectrum without and with anticoincidence
5.5 years
Energy (MeV)
(1.5  2.5 MeV): 3.3·10-3 counts/keV kg y
(~4·10-3 counts/keV kg y in H-M simul.)
C. Doerr, NIM A 513 (2003) 596
anticoincidence between 9 crystals reduces background index by factor 3
1.5 MeV
2.5 MeV
1.0 · 10-3 cts/keV kg y
Energy (MeV)

20. MaGe: cosmic ray muons - muon veto
Energy deposition in water Cherenkov detector in coincidence with Ge detectors (Ethr>50 keV)
5.5 years
Energy (MeV)
Threshold 120 MeV  all events cut but two MeV in water (~60 cm)  30,000 ph.  40 p.e. (0.5% coverage)  PMTs
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)

21. Internal backgrounds: example 60Co
1: MeV
2: MeV
: Emax = 318 keV
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)

22. 60Co background spectrum1 2
1+ 2
Q
MC simulation 
2 kg

23. 60Co: suppression by segmentation
MC simulation
Q
2 kg

24. 60Co: suppression by segmentation
MC simulation
Q
Nhit = 3
~10 (7 seg.)
Nseg = 1
2 kg
illustration:
Simple 7-fold segmentation

25. MaGe: 60Co suppression by segmentation and anti-coincidence
Number of crystals
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/r
to single unseg. detector)
N crystals = 1
Number of segments
6-3z
segmentation;
Prototype under construction
N segments = 1

26. 60Co: suppression by LAr Ge-anticoinc.
MC simulation
Q
Liquid Argon
~100
LAr anticoinc.
2 kg

27. 60Co: segmentation and LAr Ge-anticoinc
60Co: segmentation and LAr Ge-anticoinc. are orthogonal suppression methods
~1000
MC simulation
Q
Liquid Argon
Nseg = 1
AND
LAr anticoinc
2 kg

28. Experiment: LAr Ge-anticoincidence
54Mn
-source
0.18 kg
Liquid Argon
 20 cm

29. Experiment: LAr Ge-anticoincidence
Experimental Data ~5
0.18 kg
Liquid Argon
 20 cm

30. LAr Ge-anticoincidence
MC Simulation ~5
Suppression factor limited
by escape events!
Liquid Argon
 20 cm

31. LAr Ge-anticoincidence
90 cm
MC Simulation
~60
Suppression factor limited
by dead layer
0.18 kg
Liquid Argon
 100 cm

32. Status - Outlook 2004 • Feb Letter of Intent to LNGS, hep-ex/0404039
• Sep formation of collaboration
• Oct funding requests approved by MPG
• Oct Proposal to LNGS,
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

33. 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 cts / (kg٠keV٠y)
► T1/2 > 2٠1026 y , <mee> < 0.09 – 0.29 eV
phase III : world wide collaboration
► T1/2 > ~1028 y , <mee> ~10 meV

34. GERDA