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

| 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:

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

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

~10Nseg = 1

QMC simulation

Nseg = 3

60Co: suppression by LAr Ge-anticoinc.

~100LAr anticoinc.

Liquid Argon

QMC simulation

2 kg

60Co: segmentation and LAr Ge-anticoinc.

~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

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

Locations of GERDA

Infrastructures in HALL A:Super-Structure & Water tank

Infrastructures in Hall A:floor plan

NB: Sufficient access space for dismounting of LVD

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

Infrastructures in HALL A:Penthouse

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

Updated schedule (preliminary)

Updated schedule (preliminary)

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