The GENIUS dark matter project Laura Baudis Stanford University

The GENIUS dark matter project

Laura Baudis

Stanford University

The GENIUS collaboration

MPIK HeidelbergKurchatov Institute MoscowDubnaNijnii Novgorod...

Direct detection of WIMPs

elastic scattering off nuclei (Goodman, Witten 1985):

look for the energy deposited by the recoiling nucleus

0 ~ 0.3 - 0.5 GeV/cm3

v ~ 220 km/s, MB-distrib

good candidate from SUSY: LSPm = 10 - 1000 GeV< 10-41 cm2

event rate < 1 event/kg drecoil energy < 100 keV

dn/dEr

Er

Expected recoil spectrum

muon g-2 measurement

If due to SUSY:

upper bound on the neutralino mass: 500 GeV

minimum cross section is large: 10-9pb

CDMS I

CDMS II

Baltz-Gondolo 01

GENIUS

GErmanium in liquid NItrogen Setup

L. Baudis et al., NIMA 99Proposal: hep-ph/9910205

array of 40 natural HPGe detectors in Li N (100kg)

goal: reach the extremely lowbackground of 1 ev/100 kg y keVbelow 100 keV

test a large part of MSSM parameter space for neutralinos

GENIUS: detection technique

ionization in p-type HPGe detectorsno recoil discriminationsingle/multiple events give somebackground reduction

Main background reduction:

by operating naked Ge crystals directly in liquid nitrogen

Naked Ge detectors

feel well in liquid nitrogen

contacts established usingonly 3 g of material(stainless steel to fix innerand outer contacts)

here: test detector (425 g)held on kevlar wires

Performance in LiN

no electrical interferenceno microphonicsup to 6m cables betweencrystals and FETs

resolution:1 keV @ 300 keV

threshold:2.5 keV

133Babackground

Possible location: Gran Sasso

Possible layout

study in collab. with Messer-Griesheim, Germany

Design of the holder system

1,2 or moreconcentric layersof Ge crystals

holder made ofhigh molecular PE

Background expectations

Monte Carlo simulations based on GEANT3.21 + GCALOR

Geometry: 12 x 12 m tank, 2 m PE foam, 2 mm steel walls, holder system of HD1000, 40 Ge detectors, muon veto on top of the tank

External background: photon and neutron flux from rock muon interactions + induced activities

Internal background: intrins. contam. of LiN, steel vessel, holder system, Ge-crystals activation of Ge and LiN at sea level

External background

simulation of measured and n-flux in GS

Component Events/100 kg y keV

(<100 keV)

gammas 0.4

neutrons 0.04

muon showers 0.2

muon -> n 0.1

muon capture << 0.01

goal 1

12 m tank

2m borated PE foam

muon veto: 96 % eff.

Internal background

Source Radionuclide Purity Count rate/

100 kg yr keV

Liquid

nitrogen

238U232Th40K222Rn

3.5 x 10-16 g/g

4.4 x 10-16 g/g

1.0 x 10-15 g/g

3 Bq/m3

0.07

0.04

0.01

0.03

Holder

system 238U/232Th 1.0 x 10-12 g/g 0.0015

Steel

vessel 238U/232Th 5.0 x 10-9 g/g 0.08

GOAL 1

Cosmogenics in Germanium

assumptions: 10 days @ sea level 68Ge: saturration 3 yr below ground activity

3H, 49V, 54Mn, 55Fe, 57Co, 60Co, 65Zn, 68Ge

3H Q = 18.6 keV T1/2 = 12.35 yr

68Ge EC E(Ka) = 10.37 keVQEC(68Ga) = 2921 keV

T1/2= 270 d

3H, 68Ge

assumptions: 10 days @ sea level 68Ge: saturration 3 yr below ground activity

3H 3.6 Bq/kg

~113 decays/yr

200 ev/100 kg yr keV (12-19 keV)

68Ge EC 28 Bq/kg 1.1 ev/100 kg yr keV

solutions?3H: shielded production 1m heavy concrete ~ 5 mwe: factor 30 1 d transportation: factor 10 better: produce detectors in undeground lab!68Ge: decays after another 2 yr, subtract 10.37 keV line

start early with detector production, store underground

Cosmogenics in LiN

Isotope T1/2 Energy

[keV]

Activity

[Bq/g]

Rate/

100kg yr keV3H 12.3 y 18.6 (-) 3.8 x 10-8 negligible

7Be 53.3 d 477.6 () 3.7 x 10-9 0.8

10Be 1.6 x 106y 555 (-) 8 x 10-15 negligible

14C 5.7 x 104y 156 (-) 1.4 x 10-4 0.01

Goal 1

10 d transportation @ sea level

Other background sources

radionuclide production in Ge/LiN by induced sec. n:

14N(n,x)aB, 70,72,73,74,76Ge(n,x)aB

negativ muon capture in LiN -> rates and decays ofproduced isotopes:

- + (7,14) -> (6, 14)* +

(6,14)* -> (Z‘,A‘) + (1-4)n,,p

inelastic muon scattering:

+ N -> ‘ + X*

contributions are notrelevant

Expectations for GENIUS

GENIUS

CDMS Soudan

CRESST

HDMS

CDMS 2000DAMA 3

V. Mandic, R. Gaitskell

with 100 kg Ge:

detect WIMP signaturevia annual modulation

current status?

GENIUS Test Facilityis approved and being installed @ GS

Genius Test Facility

borated PE 14 natural (40 kg) HPGein a volume of 0.064 m3

of ultra-pure LiN

0.5 mm steel vessel 0.9 x 0.9 x 0.9 m polystyrene 5 cm inner shield of HPGe 10 cm low level Cu30 cm of Pb15 cm borated PE

L. Baudis et al., hep-ex/0012022

2 m x 2m

Genius-TF goals

background: 2 events/ kg y keV: 0 - 50 keV:factor of 10 better than Heidelberg-Moscow

test material purities down to this leveldesign of crystal support system new DAQ and electronicsreliability of calculation of cosmogenic productionlong-term stability of naked HPGe in LiN

Background estimations

MC simulations:

photon, neutron, muon flux in GS

intrinsic radioactivity of:liquid nitrogensteel vesselpolystyrene foamGe, Cu shieldscrystal holder systemGe crystals+ cosmogenic activation of Ge and Cu

Assumptions for material purities

Ge crystals upper limit HM

LiN 1000 x Borexino

Rn in LiN 325 Bq/m3 (Heusser 2000)

Steel Hd (Heusser 2000)

Ge bricks 100 x limit HM

Polystyrene first measurements in HD

Copper HM (cosmo + anthro)

Holder system SNO meas. for acryl

Cosmogenics in Ge30 days production + transportation @ sea level

1 year de-activation below ground

Sumspectrum

Genius-TF: expectation

based on:

2 events/kg y keV

1 yr exposure

2 keV/11 keV threshold

Genius-TF & WIMP signature

Eth= 2 keV (11 keV)B = 4 events/kg y keV M = 40 kg (nat) Ge

0.4 - 1.4 yr (1.3 - 5 yr) exposure required to see the DAMA signal with 50% - 90% probability and 99.5 % CL (S. Cebrian et al., Astrop. Phys. 14 (2001), hep-ph/9912394)

but: new detectors -> Eth= 0.5 keV!will significantly improve the sensitivity to the annualmodulation signature

good chance to see an annual modulation

Status of Genius-TF

Infrastructure built at Gran Sasso

5 detectors are ready (crystals + signal/HV contacts)

Cold hardware is being built in Heidelberg

New electronics: MPIK, Heidelberg

Setup to be installed in GS during the next months

First results expected by end of 2002

Conclusions for GENIUS

technology: simple, well understoodproduction of 40 HPGe detectors: straightforwardLiN purification method proved by BOREXINO

1 event/100 kg yr keV can be reached if:

tank diameter: 12 mproduction of cosmogenics in Ge minimizedsurface contaminations under control

cover large part of MW- parameter spacedetect a WIMP signature

backup slides

Muon induced neutrons

Negative muon capture