GERDA, the GERmanium Detector Array for the search of neutrinoless
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GERDA, the GERmanium Detector Array for the search of neutrinoless bb decay in 76 Ge. L. Pandola INFN, Gran Sasso National Laboratories for the GERDA Collaboration. PANIC Conference, Santa Fe, NM, October 24 th 2005. D L = 2 process. 0 : (A,Z)  (A,Z+2) + 2e -. p.

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GERDA, the GERmanium Detector Array for the search of neutrinoless bb decay in 76 Ge

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Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

GERDA, the GERmanium Detector Array for the search of neutrinoless bb decay in 76Ge

L. Pandola

INFN, Gran Sasso National Laboratories

for the GERDA Collaboration

PANIC Conference, Santa Fe, NM, October 24th 2005


Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

DL = 2 process

0:(A,Z)  (A,Z+2) + 2e-

p

masses of A=76 nuclei

n

W-

e-

Uei, i=1,2,3

neR

nM

neL

Uei

e-

W-

n

p

only possible if neutrino is a massive Majorana particle

coupling ~

76Ge  76Se + 2e- + 2neDL=0

~ 1021 years measured !

Motivations for 0n2b

Luciano Pandola


Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

The experiment will be hosted in the Gran Sasso National Laboratory, under the Gran Sasso mountain (Italy), 3800 m w.e.

cosmic m flux reduced of a factor 106

GERDA experiment at Gran Sasso

The GERmanium Detector Array experiment will look for 0n2b decay in 76Ge using HP-Ge detectors enriched in 76Ge

GERDA Collaboration

60 physicists

12 institutions

Italy, Germany, Russia

Luciano Pandola


Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

sum of electron kinetic energies

Sensitivity:

single site events

2039 keV

  • = detection efficiency

    a = bb isotope fraction  enrichment

    m = mass of detector in kg

    t = measurement time in years

  • B = background index in cts/(keV kg y)

  • R = energy resolution at Qbb in keV

Qbb

Advantages of Ge:

m t

  • High resolution (<4 keV @ Q)

  • no background from 2-mode

  • Signal discrimination methods

    • single site vs. multiple site events

      segmentation & pulse shape

e a

(y) > 4.3x1024

B R

@ 90% C.L.

Ultra-low background techniques available

Phased approach

increment of target mass

What do we look for?

Ge-76: source = detector (diode)

Luciano Pandola


Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

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

Qbb

> 1.57 · 1025y (90% C.L.)

The current situation

Heidelberg-Moscow at Gran Sasso

5 Ge detectors (m= 10.9 kg, a = 86%)

S = 71 kg · y , B = 0.2 c/keV kg y

Positive evidence:

= (0.69 – 4.2) · 1025 y (3s) (2004)

< mee> = 0.1 – 0.9 eV

GERDA goal: confirm or reject this claim with high statistical confidence within 1 year

IGEX at Canfranc

3 Ge detectors (m= 6 kg, a = 86%)

S = 8.8 kg · y , B = 0.2 c/keV kg y

Gonzales et al. Nucl. Phys. B (P.S.) 87 (2000) 278

Projects with other isotopes (e.g. 130Te) are also ongoing

Luciano Pandola


Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

Phases and physics reach of Gerda

Our Goal: background index 10-3 cts/(keV kg y)

10-3 / (keV·kg·y)

2·1026

(90 % CL)

10-1 / (keV·kg·y)

Phase I: existing detectors of HM & IGEX, establish background reduction

Phase II: new detectors

Phase III: worldwide new collaboration O(ton) experiment 1027 yCooperation with Majorana

3·1025

(90 % CL)

H-M bck

Phase-II

HdM & IGEX

+new diodes

Phase-I

HdM & IGEX

KK claim

2007/8

2010

Luciano Pandola


Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

... how to reach 10-3 cts/keV kg y?

The background index of10-3 counts/keV·kg·y is 2 orders of magnitude smallerthan the current state-of-the-art !

~ 0.06/cm²s (2.6 MeV )

Learn from Borexino!

Heusser, Ann, Rev. Nucl. Part. Sci. 45 (1995) 543

~5.6 m

Shield against externalgoperating naked Ge crystals suspended in high purity liquid N2/Ar

< 0.3 Bq 222Rn/m3

10-3 (kg keV y) -1

(same concept of GENIUS and GEM)

LN2, =0.8 g/cm3

Too large for GS  gradedshielding (water buffer)

Luciano Pandola


Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

Gerda baseline design

Clean room

lock

Water tank / buffer/ muon veto

Advantages of water:

- better shielding than LNitrogen

- cheaper

- safer

- neutron moderator

- Cerenkov medium for 4p muon veto

Vacuum insulated

copper vessel

Liquid N/Ar

External background

< 10-3 cnt/(keV kg y) for LN2,

factor ~10 smaller for LAr

Ge Array

Luciano Pandola


Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

water tank

top m-veto

neck

lead shielding

cryo vessel

Ge array

Backgrounds in Gerda

180 days exposure after enrichment + 180 days underground storage

derived from measurements and MC simulations

30 days exposure after crystal growing

For Phase II: B  10-3 cts/(keV kg y)  additional reduction

Luciano Pandola


Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

Background reduction techniques

  • Muon Veto

  • Anti-coincidence between detectors

  • Segmentation of readout electrodes (Phase II) (6  3z)

  • Pulse shape analysis (Phase I+II)

  • Coincidence in decay chain (68Ge)

  • Scintillation light detection (LAr option)

  • Wait for decay of isotopes (68Ge)

Luciano Pandola


Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

~14 m

14.80 m

Location of Gerda

Hall A of the Gran Sasso Laboratory, in front of LVD

Luciano Pandola


Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

Outlook and conclusions

The GERDA experiment will search for 76Ge 0n2b decay at Gran Sasso (Italy) with background level of 10-3 counts/keV kg y

Experiment approved by LNGS; substantial funding from MPI, Russia (in-kind), INFN, BMBF

Start of construction in 2006; detector commissioning/start data taking 2007

Test the result from Klapdor-Kleingrothaus in 1 year (phase I). Then phase II  2 · 1026 y

Co-operation with Majorana (MC, LArGe) very positive: mutual benefit!  Phase III

Luciano Pandola


Gerda the germanium detector array for the search of neutrinoless bb decay in 76 ge

Phases and physics reach of Gerda

Phase I:

Phase II:

Phase III:

F.Feruglio, A. Strumia, F. Vissani, NPB 659

| mee| in eV

Lightest neutrino (m1) in eV

To test inverted & degenerate hierarchy need sensitivity <50 meV

Luciano Pandola


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