Michael B. Crisler Fermi National Accelerator Laboratory

03 June 2003

The Cryogenic

Dark Matter Search

CDMS CollaborationSanta Clara University

B.A. YoungStanford University

L. Baudis, P.L. Brink, B. Cabrera, J.P. Castle, C.Chang, R. M. Clarke, A.K. Davies, M.Hennessey, M. Kurylowicz, S.W. Nam, W.Ogburn, A.Perales, T. Saab, A. Tomada

University of California, BerkeleyM.S. Armel, J. Alvaro-Dean, S. Golwala,

J. Helmig, A. Lu, V. Mandic, P. Meunier,

N. Mirabolfathi, M.C. Perillo Isaac, W. Rau,

R.R. Ross, B. Sadoulet, D. Seitz, G. Smith,

A.L. Spadafora

University of California, Santa BarbaraD.A. Bauer, R. Bunker, D.O. Caldwell,R. Ferrl, R. Mahapatra, C. Maloney,H. Nelson, R. Nelson, J. Sander, C. Savage, S. Yellin

University of Colorado at DenverM. E. Huber

Case Western Reserve UniversityD.S. Akerib, A. Bolozdynya, D. Driscoll,S. Kamat, T.A. Perera, R.W. Schnee,

G.Wang

Fermi National Accelerator LaboratoryM.B. Crisler, R. Dixon, D. Holmgren,

M. Haldeman

Lawrence Berkeley National LaboratoryJ. Emes, R.J. McDonald, R.R. Ross, A. Smith

National Institute of Standards and Technology

J. Martinis

Princeton UniversityT. Shutt

Brown UniversityR.J. Gaitskell, M.J. Attisha,

J-P.F. Thompson

University of MinnesotaP. Cushman, L. Duong, A. Reisetter

Galactic Big Picture Weakly Interacting Massive Particles

nuclear recoil~ 10’s of keV

total = 1.02

= 0.73

M = 0.27

Latest Results from WMAP Bennett et al.

b = 0.044

WIMP Velocity PlotHalo model provides reliable estimate of particle flux

(r) 0

a2+r02

=a2+r2

f(v) d3v =3/2 v0

3exp(v2/v0

2)d3v

1

0 = 0.3 GeV/cm3

a = 6.4 kpc

r0 = 8 kpc

v0 = 220 km/sec

7% annual modulation

Typical collision velocity ~ 320 km/sec

particle flux x = 0v/mx

Erecoil ~ ½ mN v2WIMP ~ 10’s of

keV

Interaction Rate

from big-bang: Density x ~ 1 / interaction rate

x ~ .3 => v ~ 10-26 cm3/s

x ~ weak

x is unknown …but we can guess

scalar interaction => NUCLEUS = A2 NUCLEON

Standard assumption:

depends only on the halo model (and on mx)

particle flux x = 0v/mx

mx is unknown …but we can guesslightest superpartner? mx ~100

GeV/c2

…Quantification of Our Ignorance

unknown mx

unknown x

Current CDMS SUF Limit

Projected Soudan Site 1 Month

Projected CDMS Soudan Limit

Your favorite SUSY models

DAMA experiment

possible signal

Technical Challenges:

Very Small Signals

characteristic nuclear recoil energy ~ 10 keV

Very Low Count Rates

expect << 1 event /kg/day

Plenty of Background

gamma, beta, neutrons from cosmic rays, contamination, radon…

CDMS Experimental Strategy

Simultaneous Measurement of Erecoil and QionizationSeparate Gamma and Beta interactions (most of the background) from true nuclear recoils (neutrons or WIMPs)

powerful new solid state detectors

Optimize our shielding design to minimize neutron backgrounds

Underground site

Stanford Underground Facility (35’, 17 mwe)Soudan Mine Underground Laboratory (2500’)

Other Analysis Handles for neutron rejection:Multiple scattering analysis (WIMPS don’t, neutrons do…)Two target materials Si for neutrons, Ge for WIMPs

Independent Monte Carlo Analysis of neutron flux

CDMS Detectors

1 cm

pure Si or pure Ge solid state detectors

very cold ~ 0.01 oKDirect calorimetric measurement of Erecoilconventional measurement of ionization Qionization efficiency Q/Erecoil --> provides particle IDelectrode segmentation for position sensitivity

Athermal Phonon Detection

localize the interaction within the crystalSpeed of sound in Si (Ge) = 1 (0.5)

cm/s

prompt phonon detection with segmented electrodes

phonons

Scattered particle

Ge crystal

Superconducting Al

tungsten sensor

phonon

Quasi-particle excitations (broken cooper pairs)

Quasiparticle Trap Assisted

Electro-Thermal Feedback

Power = V2 / R

heat

temperature

R

bias here…

Transition Edge Sensor

~80 mK

1 m

normal resistance

superconducting

ETF-TES region

The CDMS ZIP Detectors

Q inner

Q outer

A

B

D

C

Rbias

I bias

SQUID array Phonon D

Rfeedback

Vqbias

Phonon and Charge Pulses in Si and Ge

noise < 1 keV

CDMS ZIP Detector: Source Calibration

ERECOIL

gammas

ioniz

ati

on

effi

cien

cy

nuclear recoils

ERECOIL

Am241 : 14, 18, 20, 26, 60 kev

Cd109 + Al foil : 22 kev

Phonon Response … Position Sensitivity

Cd109 : 22 kevi.c. electr 63, 84 KeV

Delay Plot

A D

CB

T. Saab, Stanford U. from GSFC Talk 2002

Phonon Rise-time … Depth Sensitivity

neutrons

surf

ace

bu

lk

gammas

n

(WIMP)

electrons

Incomplete charge collection at the surface

1999 Data Set …3 pre-ZIP Ge DetectorsInner-Electrode Shared-Electrode

Shared-electrode

B4

B3

B5

B6

Inner-electrode

All 1998/1999 data consistent with neutrons only

, except…

23 events consistent with WIMPs

ioniz

ati

on

effi

ciency

ionization efficiency

4 double scatters…

1998 Data Set …1 Si ZIP

4 events on Si…

CDMS I->II• Go deep underground• Athermal phonon technology

– Even better rejection of background

• Increase the mass -> 7kg– 7 towers of 6 detectors

• Approved in January 2000

2001/2002 Data Set …full tower 4 Ge, 2 Si ZIPs

28.3 kg-days for WIMPs20 Ge nuclear-recoil candidates > 5 keV

increased polyethelene shielding reduced neutron flux by 2.3

non-neighbor double scatterstriple scatters !

Again consistent with neutrons only

2 Si events

CDMS Sensitivity (Stanford Underground Facility)

CDMS 1998/99

DAMA

no subtractionCDMS new…

Edelweiss !

30 feet

Stanford U. Campus

2500 feet

Downtown Ely, Minnesota

T. Saab, Stanford U.

(shown here during rush hour…)

Soudan Shielding Assembly

Pb Lid in Place

Cryo Plant in Place (CDMS WEBCAM)

Source Calibration (CDMS WEBCAM)

Veto Shield in Place (CDMS WEBCAM)

CDMS Status / Summary

Beam Continues to Run Smoothly…

Expect Data this Summer

including the one used for data taking at Stanfordsystem has been cold and fully operational. One more cryo bug…

Two Full Towers of Detectors in Place at Soudan

…only 2465’ further underground

with the exact same apparatus…

Much excitement about repeating this measurement