The Ge Detector Array for the search of 0νßß decay in Ge...

3800

m.w

.e.

Karl Tasso KnöpfleMPI Kernphysik, Heidelberg

[email protected] A of

LNGS

GERDA The Ge

Detector Array for the search of 0νßß

decay in Ge-76

-

recent progress -

SNOLAB Workshop, Sudbury, 4 –

5 October 2008

mailto:[email protected]

SNOLAB 08 K.T.Knöpfle: 'GERDA' 2

~ 95 physicists from 17 institutions

The GERmanium

Detector Array Collaboration

http: //www.mpi-hd.mpg.de/GERDA



The GERmanium

Detector Array Collaboration



OUTLINE• Introduction• Progress on

cryostat & cryo-infrastructurewater tanklab building & platformGe

diodes & electronic readout

• Conclusions


attractiveness of Ge-76

• Ge

semiconductor ► source & detector

• intrinsic Ge

material ► purest available solid state material

• established enrichment

from 7.44% (nat.) to 86% , affordable

(2005) at ~50$ / g

• very good energy resolution, <0.2% at 2039 keV

► narrow ROI of 4 keV

►negligible overlap with 2νßß

background; ~(2·10-3)6

for same T1/2

• favorable product of phase space factor & nuclear matrix element

last not least:

best limits on resp. claimed evidence of 0νßß

decay(Cuoricino, however, reporting now very similar limit!)

Exp. Isotope mass/enrichment Qßß

/ resolution B (cts

/ kg•yr•kev) CUORE

Te-130 741 kg / 34% 2528 keV

/ 0.28% ~10-3

EXO Xe-136 200 kg / 80% 2479 keV

/ 1.4%

10-2

– 10-3

GERDA Ge-76 18-40 kg / 86% 2039 keV

/ <0.2% 10-2

- 10-3


<mßß

> best limits* / valueKKDC: H.V.Klapdor-Kleingrothaus, I.V.Krivoshina, A.Dietz, O.Chkvorets, Phys.Lett. B586 (2004) 198Heidelberg-Moscow

Qββ

?

Bi-214 Bi-214

5 enriched Ge-76

diodes (10.9 kg / 71.7 kg٠y)‘Background Index’

B = ~0.1 cts

/ (keV٠kg٠y)

T1/2

= (0.69 -

4.18)٠1025 y (3σ range)0ν

IGEX

: Gonzales et al., NP B87(2000)278

► confirmation needed with same & different isotopeskey: reduce background

by O(100) for better sensitivity

* Cuoricino

has reported similar limits for Te-130

8.5 kg٠y


GERDA goals & sensitivityGERDA’s

goal : reach background index at Qββ

= 2039 keV

of 0.01

/ 0.001

cts

/ (keV٠kg٠y)

• phase I : use existing Ge-76 diodes of Heidelberg-Moscow experiment & IGEX (~18 kg)~ 0.01 cts

/ (keV٠kg٠y) intrinsic background expected• phase II

: add new enriched Ge-76 detectors, ~20 kg , (37.5 kg enriched Ge-76 bought) ~ 0.001 cts

/ (keV٠kg٠y) background expected ► 3 y٠35 kg• phase III: depending on results worldwide collaboration for real big experiment

close contacts & MoU

with MAJORANA collaboration established

KKDC

KKDC

measured deduced mass hierarchy

A.Strumia

& F.Vissani, hep-ph / 0503246

degenerate

normal

inverted

0.01 0.01

0.001

0.001


background reduction EXTERNAL bgnds: γ(Th, U), n, μ

Ø 10 m

Ø 4 m

H 1

0 m

water: γ

& n shield, Cherenkov mediumfor μ

veto

LArstainlesssteel cryostatw Cu shield,Rn

tight

also active shield !

α(LAr) = 0.050/cmα(H2

O) = 0.043/cmα(Cu) = 0.34/cmα(Pb) = 0.48/cm

INTRINSIC or VERY CLOSE bgnds

: cosmogenic

-

60Co (5.3 a), 68Ge (270 d)-radioactive surface contaminations Shielding

possible

.

bare Gediodes

► anti-coincidence of detectors &detector

segments► pulse shape discrimination (PSD)

Discriminate single & multi site events !► SSE: ßß, DEP ►MSE: Compton

signal background

array of segmented Ge

detectors

γ


designer’s view of GERDA in LNGS Hall A▲ 3800 m.w.e. rock above ▲

7 strings

phase

I

phase

II


cryostat

& cryogenic

infrastructure


t

08 March 06

arrival of cryostat in Hall A


cryostat performancespecso double-walled, super-insulated, 1.4571 ss

steel,o volume 65 m3 LN/LAr, o environment of 8m water heighto operating pressure 0.2 bar overpressure

measured performance:o thermal loss 200W o Rn

emanation rate: 14 / 35 mBq

before/after Cu mount► final cleaning cycle needed ( 8(12) mBq

≡

BI=10-4

)

safety features:o detailed risk analysiso no penetrations in cryogenic volumeo designed for 1.5 bar overpressure acc. AD2000 codeo extra thermal insulation to limit evaporation rate in

case of leakage of one wall

special features:o

internal copper shield for improved BIo

active cooling with LN2 to avoid LAr

refills

active cooling

t=3/6 cm copper

SNOLAB 08 K.T.Knöpfle: 'GERDA' 1207 December 04

inst

alla

tion

supe

rinsu

latio

n


parallel to SI installation

Rn

emanation test

05dec07


cryostat integration

8 support

pads


centering of pads

1 of 8


Bosche

type KSB 2000 (kg) load cells

Al plate

preparations for load test


Al plate

bottom of outer vessel


t

load test in progress

12dec07


load test

Al plate

bottom of outer vessel

stiffness of Belleville springs:59 kN

/ mm each

results


evaporation test

GN2

flow meter

heater

LN225 m3

LN2

evaporation

test


evaporation test

spec.: ~ 4m3 N2@20deg ( = 300W)

24jan08 9:07

25jan08 12:14

nice result !


t

08 March 06

unloading of cryostat


t

08 March 06

cryostat placed in Hall A

LVD

SNOLAB 08 K.T.Knöpfle: 'GERDA' 24set up for coppershield installation

©

Cattadori

jun.


t


mounting tool for copper shield

‘tripod’

internal platform

copper plate

tent

rotatable arm

platform 4x4 m2


t


Progress

27 Feb :

pressure test of outer vessel 1.85 barg

N2Feb : cryostat filled with Rn-free nitrogen (for Rn

test)

03 Mar : cryostat leaving SIMIC06 Mar : arrival & installation in Hall A of LNGS

11 Mar : Rn-222 emanation test, 2 extractions (44/40m3) 13.6±3/13.7±3

mBq

18 Mar : internal copper shield installed

04 Apr : LN2 evaporation test of completely filled cryostat <4Nm3/h (<300W)09 Apr : 21:35 cryostat again empty (3.6/3.2/2.9 @3/6/9 pm)

28 Apr : start of WT construction

03 May: Rn-222 emanation test, 2 extractions (26/20m3)

121±5/120±5

mBq

27 Jun: Rn-222 emanation test, 2 extractions (30/21m3) 33±8/36±9 mBq


s final PID of cryogenic

infrastructure

valve

box

triax

line

forLN2

& LAr

stor

age

tank

s

to heater

LN2

LAr


valve

box

Rn trap

&particle

filter

in LAr

line


Argon extraction system

in Hall A

heater

cryogenicstoragetanks

LVD

GERDA

designed

for

10000 m3/h


TEMA BEU heater


water

tank


construction steps

1

3

2

last

build

roofand topcylindricalsegment

lift

build

top-1cylindricalsegment

weld

alwaysat ~2.5m level


s

08 May 05


status:

08 May 20

construction of water tank


s

08 May 28


lab building

& platform


status: construction of GERDA bldg & platform

08 July 17

CUORECRESST


s

08 September 19 2nd floor


next steps

another

cleaning

cycle

of cryostatinstallation

of part

of cryogenic

infrastructure

cleaning

of water

tankwater

drainage

test ?

installation

of VM2000 foil

& photomultipliers

construction

of cleanroominstallation

of heater

installation

of comissioning

lock

LAr

fill

2008

2009


Ge diodes

& electronic

readout


R&D: long term stability of Ge

diodes in LArProblem* of ‘Limited long-term stability of naked detectors in liquid nitrogen as result of increasing leakage current’

resolved by GERDA:• 2 years of operation of HPGe

detectors in LN/LAr• >50 cooling/warming cycles done► detector handling procedure defined

(closed volume, clean N2 atmosphere)► reduction of passivation

layer reduces radiation-induced increase of leakage current.

* Klapdor-Kleingrothaus

& Krivosheina, NIM A566 (2006) 472

10 pA continued

no deterioration after 1 year of operation in LAR


R&D: phase II detectors

• 37.5 kg of enriched Ge

(86% Ge-76) have been procured by MPI Munich and are stored underground.

• Natural Ge-dioxid

has been reduced to metal and purified to 6N material for Czochralski

pulling• First Ge-nat

crystal pulled with dedicated puller at Institut

für

Kristallzüchtung

(IKZ) at Berlin

• 3x6-fold segmented protoype

detectorworks fine: 3keV resolution at 1.3 MeVfor both core and segments

• Novel low mass contacting scheme verified (Abt

etal, NIM A577 (2007) 574)

• Functioning of contacts also verifiedin LN2, good energy resolution w/ooptimization

Interesting alternative: ► point contact detector


R&D : pulse shape discrimination (PSA)

coaxial

modifiedelectrode

• Non-segmented but powerful PSD • most interesting candidate if massproduction feasible

Luke et al. , IEEE TNS 36 (1989)Barbeau

et al., nucl-ex/0701012v1

modified electrode detector


R&D: SSE/MSE discrimination

examples Th-228 BEGe

point-contactdetector (Canberra)

3x6-fold segmented coax detecor

91%

82%

log

scal

es

13%

19%

Qßß

49%

48%

Abt

etal

NIM A583 (2007), Eur.J.Phys. C52 (2007)

D..Budjas

13%

14%

fractions after PSA cut

fractions after single-segment & PSA cut

2nd

escape peakphoto peak


R&D: ASIC preamplifier for 77

K

• built in AMS HV 0.8 μm CZX

• input FET, Rf

& Cf

discrete

• 15 ns rise time with 10m coax cable

measured spectrum at 77K

Equivalent noise charge at 77K (300K) cold warm

PZ-0

PZ-0


summary

*

with nucl. m.e. from Rodin et al.

• approved in 2005 by LNGS with its location in hall A,• funded by BMBF, INFN, MPG, and Russia in kind• construction in LNGS Hall A soon to be finished• all phase I detectors (8 pcs

,~18 kg) refurbished & ready

• parallel R&D for phase II

• 2008 / 09 ► continue / finish installation, do commissioning

goals:

phase I : background 0.01 cts

/ (kg٠keV٠y)► scrutinize KKDC result within ~1 year

phase II : background 0.001 cts

/ (kg٠keV٠y)► T1/2

> 1.5٠1026 y , <mee> < 0.2 eV *


finis / backup slides


screening of cryostat’s ss* sheetsresults from γ

spectroscopy at LNGS and MPI HD

► NIM A593 (2008) 448

sheets for i. / o.cylindrical walls

Co-60

unexpected low Th-232 activity, typ. <1 mBq/kg ► less massive Cu shield needed

sheets for inner/outervessel heads

@ SIMIC

Th-232#1

#1

#2

#2

#1i

#2i

#2i

*1.4571 or X6CrNiMoTi17-12-2.

The Ge Detector Array for the search of 0νßß decay in Ge...

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