gerda neutrinoless double beta decay

GERDA

NeutrinolessDouble Beta

Decay

Ludwig Niedermeier, Universität Tübingen NPAE Kiev, 1.6.2006

20 conditions:

Majorana particle

r↔l helicity flip

~(1-(v/c)2) for m>0

Neutrinoless Double Beta Decay

20 decay

n

n p

p

e-

e-

W-

W-

22 decayn p

n p

e-

e-

W-

W-

l

r

_

r

_

r

_

= _

E (e–+e–) in keV

From Decay to Neutrino Mass

• Exp. determination of 20 half life with 76Ge

=> Effective neutrino mass: determination / limit

00

1/ 22 0

01/ 2 20 2

0

32

1

ln 2ln 2 ln 2 ln 2

1

( , )

S

oee

ee en nn

amN N a mtMTS M b EB bmt E

tt t

with TG E Z m

and m U m effective mass

N Number of Ge atomsS 20 signalB Background signalsb Bgr. rate (kg s keV)-1

m Ge massM Ge mol. weighta 76Ge enrichment Detection efficiencyE Energy binningt Measurement time

(inverse)

(normal)

Impact on Neutrino Physics

Hd-Moscow

GERDA I

GERDA II

GERDA III (???)Current status:

m²12 ≈ 8·10-5 eV² (solar )m²23 ≈ 2·10-3 eV² (atm. )

normal hierarchy or inverse hierarchy ? 3 1

1

2

2

3m12

m23

m12

m23

m in

eV

↔meeabsolute mass scale

The Heidelberg-Moscow-Experiment

[Klapdor-K. et al, Phys.Lett. B586(2004)198]

Best fit:T2β0= 1.2·1025 y

A.M. Bakalyarov, A. Ya. Balysh, S. T. Belyaev, V. I. Lebedev, S. V. Zhukov (Kurchatov Institute, Moscow):

T1/2(2β0ν) >1.55 · 1025 y (90% C.L.) [Письма в ЭЧАЯ. 2005. T.2, No.2(125). C.21-28]

76Ge

Gerda – Detector Overview

Water shielding Cherenkov muon veto

LN2 or LAr shield

76Ge crystals

Gran Sasso laboratory3600 mwe

– Check of Hd-Moscow publications– Further improvement of mee sensitivity

Gerda - MotivationHd-

Mos

cowG

ERDA

Reduce background by ultra-pure shielding material LAr or LN2

surrounding Ge crystals 0.17→~10-3(kg·y·keV)-1

Phase I 5 crystals of HD-Moscow, 3 of IGEXm76Ge = 18kg t ≤ 1aBackground requirement: 10-2 (keV kg y)-1

Phase II Additional crystal insertionm76Ge=37.5kg (a>86%) t = 3aBackground requirement: 10-3 (keV kg y)-1

Phase III (?) World-wide collaboration (contact with MAJORANA)

m76Ge ~ 500kgBackground requirement: 10-4 (keV kg y)-1

1.2 · 1025

Gerda – Development

Results!

Gerda – Background

anti-coincidencepulse-shapedecay chain coinci-

dence for 68Ge

anti-coincidence with crystal segmentation

Required background level (phase I): 10-2 (keV kg y)-1

(phase II): 10-3 (keV kg y)-1

Compare Hd-Moscow 0.17 (keV kg y)-1

(97% veto)

(30d exposure)

Gerda – Ge Crystals

Phase II – ≈20 crystals

1 crystal – 18 segments

Gerda Muon Veto –A Water Cherenkov

Detector

plastic scintillator

photomultiplier

cryo tank + 3.wall

water tank

reflector VM2000

‚lower pillbox‘

Ge crystals

The LArGe Facility as Test Bench

Test bench at LNGS for refurbished Ge detectors and Liquid Argon solution

LAr LN2

better shield better n shieldscintillation veto less scattered n

no 39Ar contam. TEST! easier handling

Cryostat (1.3m³)

Cu shielding

Pb shielding

Gerda – Schedule

o Ge refurbishment/testing in LArGeo Start of construction in fall 2006o Construction of cryo tank (→ stainless

steel)o Construction of water tanko Insertion of muon vetoo Insertion of first Ge crystals in Gerda

(Phase I)o Towards Phase II: Insertion of more

crystals (37.5kg of enriched 76Ge already produced)

o Final detector fillingo Data taking (3 years)

o Phase III (?)

Construction

Phase I

Phase II

Phase III

Gerda – Conclusion

Test of the Klapdor-Kleingrothaus et al. publication result

Aim to mee determination

Phase I: mee → 0.3 eVPhase II: mee → 0.1 eVPhase III could check inverse hierarchy

Gerda – Collaboration INFN Laboratori Nazionali del Gran Sasso, Assergi, Italy Joint Institute for Nuclear Research, Dubna, Russia Max-Planck-Institut für Kernphysik, Heidelberg, Germany Jagellonian University, Krakow, Poland Università di Milano Bicocca e INFN Milano, Milano, Italy Institute for Nuclear Research of the Russian Academy of

Sciences, Moscow, Russia Institute for Theoretical and Experimental Physics, Moscow,

Russia Russian Research Center Kurchatov Institute, Moscow, Russia Max-Planck-Institut für Physik, München, Germany Dipartimento di Fisica dell’Università di Padova e INFN Padova,

Padova, Italy Physikalisches Institut, Universität Tübingen, Germany EC-JRC-IRMM, Geel, Belgium