Phase I:• Use available 76Ge diodes from Heidelberg-Moscow and IGEX experiments (~18 kg).• Scrutinize with high siginificance current evidence.

Phase II:• Add new diodes up to 40 kg mass of 76Ge.• Segmentation of detectors.

Long-term future (Phase III):• World-wide collaboration: O(500 kg) experiment.

The GERDA experimentThe GERDA experimentGERDA collaborationGERDA collaboration

The GERDA collaboration

Max-Planck-Institut für Kernphysik / Heidelberg

European collaboration of the following institutes:• INFN Laboratori Nazionali del Gran Sasso, Assergi/Italy• Jagellonian University, Cracow/Poland• Joint Institute for Nuclear Research, Dubna/Russia• Institute for Reference Materials and Measurements (IRMM), Geel/Belgium• Max-Planck-Institut für Kernphysik, Heidelberg/Germany• Institut für Kernphysik, Universität Köln/Germany• Università di Milano Bicocca e INFN Milano, Milano/Italy• Institute for Theoretical and Experimental Physics, Moscow/Russia• Institute for Nuclear Research of the Russian Academy of Sciences, Moscow/Russia• Russian Research Centre Kurchatov Institute, Moscow/Russia• Max-Planck-Institut für Physik, München/Germany• Physikalisches Institut, Universität Tübingen/Germany

• forbidden in the standard model (Lepton-number violating process).• Only possible if is massive Majorana particle.• Signature is peak at Q-value of decay.

4.2 evidence for -decay reported for 76Ge (Q-value: 2039 keV):Klapdor-Kleingrothaus et al., NIM A 522 (2004) 371-406.

GERDA design and sensitivity

Water tank(Muon-veto)

Cryostat

Cleanroom

Ge-detector array

Cryogenic liquid

Neutrinoless double beta decay

Background reduction and suppression techniques

( also see dedicated posters)

Material screening:Cryogenic gas purification

• -screening with ultralow background Ge-spectrometers.• GeMPI at Gran Sasso reaches few ten Bq/kg level.

• Large scale N2 purification plant at Gran Sasso: 222Rn in N2 <0.5 Bq/m3.

• Recent result:Ar can be purified to same purity level as N2.

Detector segmentation

• -decay is single-side event.• Double-side background events can be discriminated by detector segmenation.

Phase I activitiesPrototype detector operations Opening of enriched detectors

Phase Idetector array

Goal: Spectroscopic performance of the detector assembly in a radon-free test bench: Same resolution achieved for bare crystal as measured in the cryostat.

Heidelberg-Moscow detector ANG I

IGEX detector RG III

2 76Ge-diodes have been removed from their cryostat and measured.

Both diodes have been refurbished and are stored underground again.

• R&D project for low background detector operation in liquid argon.

Lock

Lead

Steel

Poly-ethylene

Copper

Liquid argon

PMTs

Phase II detectors

Example:63z segmentation and achieved background reduction for a 60Co source.

The LArGe facility

• 37 kg of enriched Ge for new 76Ge diodes already produced in Russia.• Segmented, true coaxial n-type detectors.• Signal from each segment and core signal are read out separately.• Extremely low mass support structure.• Special suspension system.• First segmented prototype detector successfully operated.

Muon-induced backgroundPrompt background (without -veto)

Energy (keV)

Anticoincidence(phase I): 10-3

Segmentation(phase II): 3·10-4

Counts

/kg

/keV

/y

goal

no cut: 10-2

• Goal is not achievable without muon-veto.• But 75% efficient muon-veto is sufficient.• Water Čerenkov veto with light reflector foil (VM2000) is expected to be more efficient.

Backgroundin LN2

[cts/(kg·keV·y)]

Backgroundin LAr

[cts/(kg·keV·y)]

77,77mGe 1.0 · 10-5 1.1 · 10-4

Others 5 · 10-6 5 · 10-5

Delayed background

• Background goal 10-4 cts/(kg·keV·y) can be achieved for LN2.• More neutrons produced in LAr Background above 10-4 cts/(kg·keV·y).• Goal can be met by delayed coinci-dence cut (muon, -rays, -decay).

MC simulation

Operation of bare 76Ge diodes in ultrapure cryogenic liquid (LAr/LN2).

Contaminations from cryostat/ crystal holder can be avoided.

Low mass detector suspension and holder made out of carefully selected materials only.

Experiment will be performed in the Gran Sasso underground lab.

Assumption: E=4 keV