The Heidelberg Dark Matter Search Experiment

Laura Baudis

Stanford University

The HDMS collaboration

MPI fuer Kernphysik, Heidelberg

Group of Prof. H.V. Klapdor-Kleingrothaus

The HDMS detectors

2 HPGe detectors in one

cryostat system

inner: WIMP target

outer: active veto

against multiple Comptons

passive Ge shield

WIMP

gamma

Property Inner Detector Outer Detector

Crystal type p-type n-type

Mass [g] 202 2111

Active vol [cc] 37 383

Diameter [mm] 35.2 84.4

Length [mm] 40.3 86.2

Op. bias [V] + 2500 -1500

FWHM @ 300 keV

(1332 keV) [keV]

1.2 (1.87) 3.2 (4.45)

Threshold [keV] 2.0 7.5

Some detector properties

Cross talk between detectors

linear correlation:correction offline

kio = 0.00375 +/- 0.43 x 10-4

koi = 0.12850 +/- 0.27 x 10-3

Cross talk induced error

compare zero energy resolutions:

inner: no effectouter: from 0.3% to 0.4% at 1332 keV

The HDMS detector

HDMS in Gran Sasso

prototype: March 98-July 99

Performance @ GS

stable running over ~ 15 months

individual runs ~ 0.9 dchecked daily: leakage current nitrogen flow overall trigger individual count rate, etc

weekly: calibration with 133Ba, 152Eu-232Th source

Outer detector: 363 raw live-d

68Ge, 57Co, 58Co, 54Mn, 60Co, 65Zn, 137Cs, 238U, 232Th, 40K

Inner detector: 363 raw live-d

68Ge, 54Mn, 57Co, 60Co, 210Pb, 212Pb, 214Pb, 40K

Background model

MC simulation of dominant backgrd. MC simulation of dominant backgrd. sources with extended GEANT3.21sources with extended GEANT3.21

Inner: low energy spectrum

68Ga X-ray

49Ti, 55Mncross talk?

Structure at 32 keV: cross talk?

Anticoincidence between inner and outer

Eth for anticoincidence: 3 sigma away from zero

threshold

[keV]

FWHM/2.35

[keV]

inner 2.0 0.40

outer 7.5 1.42

40-100 keV: factor 4.3

11-40 keV: 0.2 events/kg d keV40-100 keV: 0.07 events/kg d keV

3

1.2 keV

4.3 keV

HDMS prototype limits

only last 49 d of data taking: 9.9 kg d2-30 keV: 0.5 events/kg y keV

L. Baudis et al., PRD63,2000

73Ge-HDMS: full scale

inner crystal replaced by 73Ge crystalsensitive to spin-dependent interactions70Ge de-enriched by factor >50new copper holder systemno soldering of contacts

installed in GS: August 2000working wellfirst analysis: fall 2001?expectation: test DAMA withindependent technique and raw data

HDMS goal

Based on: 0.07 events/kg d keV in 2 - 30 keV region

Conclusions

HDMS prototype worked welllimits competitive to other Ge experiments

73Ge-HDMS installed in August 2000first 73Ge detector!first data to be analyzed soon...independent test of DAMA region sensitive to spin-dependent interaction

however, increase of target mass improbableno sensitivity to a WIMP signature