M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005

M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005

Investigating Neutrinoless Double Beta Decay

Status of the GERDA ExperimentMichael Altmann

Max-Planck-Institut für Physik, Munich

Physics

Concept

Exp. Setup

R&D DetectorsSchedule, etc.Summary


Physics Motivation : Nature of the Neutrino

Neutrino masses and lepton flavour mixing established by oscillation experiments

Neutrino mass differences known

Still Unknown: absolute mass values

hierarchy scheme

= anti- ?

Neutrinoless Double Beta Decay


Physics Goals and Experimental Requirements

For excluding inverted hierarchy:Sensitivity on 10 meV level required ton-scale @ B < 10-4 / keV kg yr

Phase 1

Phase 2

Phase-3

GE

RD

A S

en

sitiv

ity

Klapdor-Kleingrothaus positive evidence


GERDA: Germanium Detector Array

Array of HP-Germanium Diodes, made from isotopically enriched (86% in Ge-76) material

Phase-1:Use existing diodes from Heidelberg-Moscow and IGEX ( 15kg)0.01 / keV kg yr intrinsic background expectedGoal: verify concept; probe Klapdor-Kleingrothaus‘ evidence (if no event observed, 1 yr of measuring time needed to disprove at 98% cl)

Phase-2:Increase mass by adding 20 kg of new enriched Ge-detectorsGoal: 100 kg yr statistics at background level B<10-3 / keV kg yr

T1/2 > 2 * 1026 yr meff < 0.09 – 0.29 eV

Phase-3:(Depending on results of phase-2 and possibly other experiments)worldwide collaboration for really big experiment; close contacts and MoU with MAJORANA established


GERDA‘s Experimental Concept Assumption: External background is

dominant• Minimize all impure materials close to Ge diodes• Operate Ge diodes in ultraclean environment cryogenic liquid shield (LN or LAr); graded shielding

• Reject remaining background (internal and external) by exploiting different interaction topology (single-site multi-site; PSA)

Goal: Background index of 0.001 cts / (keV kg y) at Q=2039 keV


GERDA Location: Gran Sasso National Laboratory (LNGS)

GERDA1400 m ~ 3.800 m.w.e

Assigned Location for Phases 1 & 2: LNGS Hall A, next to the CRESST and LVD Experiments


Experimental Setup at LNGS


GERDA‘s Cleanroom Facility at LNGS: LArGe

HD-Moscow‘s KI-detectors were handed over to GERDA


LArGe‘s Liquid Argon Test Stand


Detector Arrangement

Modular Detector Arrangement :- Detector strings

- Hexagonal string arrangement

- Low mass, low background crystal holders and suspension- Additional strings can „easily“ be added when new detectors become available, with the vessel remaining cold


Detector Suspension for Phase-1

- Low mass (bgd index < 10-2 / keV kg y )

- Use only screened materials with known radioimpurities (Cu, PTFE, Si)- Specific ORTEC-type contact (bottom of bore hole)- Mount and test every crystal individually (LArGe Facility at LNGS)


Ge-76 Procurement for Phase-2

- Enrichment of 37.5 kg of Germanium ongoing (ECP, Krasnoyarsk, Russia)

- Delivery procedure tested with natGe: very smooth, no problems encountered (20 day trip Krasnoyarsk Munich, special shielding container: 10-20 attenuation factor for cosmogenic production of 68Ge and 60Co)- ongoing R&D: maintaining original purity during enrichment

optimizing yield of chemical purification to 6N metal


Phase-2: Segmented DetectorsInteraction topology of -signal and -

background different anticoincidence for bgd suppression„pointlike“, single-site vs. „extended“, multi-site

60Co: 2 photons (=O(cm))

(multiple) Compton-scattering

2 electrons deposit energy locally (d = O(1 mm))


Detector Development for Phase-2R&D on two types of detectors: p-type and n-type

n-type prototypes: Naked crystal: available & operated in LN Naked crystal, 6x3z segmented, true coax: on orderp-type prototypes:

Naked crystal, true coax: available & operated in LN

Naked crystal, true coax, 6x 1z segmented: available Naked crystal, true coax,

6x 3z segmented: on order


Detector Suspension for Phase-218-fold segemented

detectors (true-coaxial, 3x6, n-type)

Kapton cable

bonded contacts

Total of 30g mounting material / detector


Simulation Results on Segmented Detectors

- Monte Carlo (MaGe: common Majorana-Gerda simulation framework) : Anticoincidence between segments (18-fold segmentation)

factor 10 increase in 60Co rejection

- Further improvement (up to factor 5):Analysis of pulse shapes and mirror charges (PSA)( regain signal sitting on segment boundary)( 0.2 cm spatial resolution)

- R&D ongoing: Monte Carlo studies and PSA development Laboratory measurements with prototype

detectors


Pulse Shape SimulationFull simulation of true coaxial 6-fold segmented detector (only 1 segment hit):

electrode electrode electrode

electrode electrode electrode

core

Cha

rge

Time

Hit segment:full energy deposit

Core signal: full energy deposit

Neighbouring segments:mirror charges


Full Simulation of a True-Coax 18-fold Segmented Detector

Signals seen by the segment electrodes Position Reconstruction ( and z)


Simulation Results on Segmented Detectors

PSA Information on radius and angle:

Clear correlation between time of charge collection and radius of interaction point

Correlation between ratio of amplitudes of neighbouring segments and angle of interaction point


Status & Time Schedule2004:• Feb Letter of Intent to LNGS (hep-ex/0404039)• Sep Formation of Collaboration• Oct Funding request approved by MPG; Proposal to LNGS (wwwgerda.mppmu.mpg.de)

2005:• Feb GERDA approved by LNGS• Mar Technical proposal to LNGS; 30 kg of enriched Ge-76 for phase-2 ordered• May Funding requests approved by INFN• Jun Funding request approved by BMBF• Jul Ge-76 order enlarged to 37.5 kg; safety study for cryostat submitted to LNGS• Aug Expect decision by LNGS on system safety• Sep if OK: tendering for water tank, first orders for cryostat

2006:• Jun Start of water tank installation at LNGS• ??? Installation of cryostat, clean room and lock, muon veto, ...

2007:• spring Commissioning, then start of physics run


The GERDA Collaboration


Summary and Conclusions

Approved by LNGS with location in hall A

substantially funded by BMBF,MPG, INFN and Russia (in kind) construction at LNGS start 6/06

in parallel: substantial R&D for and preparation of phase II start of data taking in 2007

phase-1: verify concept, probe KK-evidence for 0phase-2: T1/2 > 2 * 1026 yr m

eff < 0.09 – 0.29 eV phase-3: t.b.d., depending on results; ton-scale experiment in worldwide collaboration

Documents

M.Altmann, GERDA Status Report SNOLAB Workshop IV, 15.-17.8.2005