First Results from the Cryogenic Dark Matter Search at the Soudan Underground Laboratory
description
Transcript of First Results from the Cryogenic Dark Matter Search at the Soudan Underground Laboratory
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
First Results from the Cryogenic Dark Matter Search at the Soudan
Underground Laboratory
Priscilla CushmanUniversity of Minnesota
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Composition of the Cosmos
WIMPsWMAP best fit
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Moving from a Shallow Site at Stanford to a Deeper Site at the Soudan Underground Mine in Northern Minnesota
1 per minute in 4 m2 shield
Depth (mwe)
Log 1
0(Muo
n Fl
ux) (
m-2s-1
)
Stanford Underground Site500 Hz muons in 4 m2 shield
Depth 713 m (2090 mwe)Reduce neutron background from ~1 / kg / day to ~1 / kg / yearReduce cosmic muon flux by ~ 30,000
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Brown University M. Attisha, R.J. Gaitskell, J.P. Thomson, Case Western Reserve UniversityD.S. Akerib, M. Dragowski, S. Kamat, R.W. Schnee, G.WangFermi National Accelerator LaboratoryD. Bauer, M.B. Crisler, D. Holmgren, E. RambergLawrence Berkeley National LaboratoryJ.H. Emes, A. SmithUniversity of Florida
L. BaudisSanta Clara UniversityB.A. Young
University of Minnesota, MinneapolisL. Duong, P. Cushman, A. ReisetterStanford UniversityP.L. Brink, B. Cabrera, C.Chang,R.W. Ogburn
University of California, BerkeleyV. Mandic, P. Meunier, N. Mirobalfathi, B. Sadoulet, D. Seitz, B. Serfass, K. SundqujstUniversity of California, Santa BarbaraR. Bunker, D. O. Caldwell, R. Mahapatra, H. Nelson, J. Sander, S. Yellin.
University of Colorado at DenverM. E. Huber
The CDMS Collaboration
…in the mine
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
The Soudan Underground Laboratory
MINOS
CDMS II
Old: Soudan2 proton decay calorimeterNew: Screening and Prototyping Area Applications welcome, see
http://www.hep.umn.edu/~prisca/soudan
Operated by the University of Minnesota, in cooperation with Fermi National Accelerator Laboratory
and the Minnesota Department of Natural Resources
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Dan BauerNSF/DOEOct. 8, 2002Soudan Installation
¥ CDMS II Experimental Enclosures ( Fermilab, Minnesota)
H V A C
M e c h a n i c a l
R F - s h i e ld e dC lean room
Shield
F ridge
F ro n t-e n dElectronics
Mezzanine Mezzanine
D etecto r P rep
D A Q /E l e c tro n i c s
Clean BenchesIceboxP um ps,C ryo gen ics
Soud
an
2
Mino
s en
tranc
e
Dan BauerNSF/DOEOct. 8, 2002
CDMS II Facilities
Mezzanine
Main floor
Electronics roomClean Room Loft
Offices
MINOS staging
Detector Prep
Cleanroom
Main floor
Mezzanine
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
CDMS Icebox and Shield
plasticscintillators
polyethylene
lead
ancientlead inner
polyethylene
Dilution Fridge
|------------------ 2.18 m --------------------------|
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Q inner
Q outer
A
B
D
C
Rbias
I bias
SQUID array Phonon D
Rfeedback
Vqbias
ZIP Detectors and Tower Construction
4 Phonon Channels: XY position Z position using timing and signal shape 2 Charge Channels: radial position
250 g Ge or 100 g Si crystal1 cm thick x 7.5 cm diameter
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Detector Traces & Event Reconstruction
• Charge rise time is fast (~ 1 us) compared to the phonon rise time (~10-20 us)• Phonon pulse time of arrival allows for event position reconstruction• Event energy reconstructed using optimal filter (time => FFT => fit in freq)• Example of a typical 20 keV event in a Si & Ge ZIP
(very good signal/noise for a 20 keV true recoil energy event)
Si ZIP Ge ZIP
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Discrimination of nuclear recoils to electron recoils
Yield = Ionization Energy Total Recoil Energy
Calibration Data
Surface betas are electron recoils with reduced charge collection
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Timing provides further discrimination
Use phonon risetimen-recoil is slower than e-recoil
AndCharge to phonon delay
smaller for surface e’sgammas
neutrons
Ejectrons=e- products of incident radiation
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Phonon energy in keVPhonon energy in keV
Excellent agreement between data and Monte CarloExcellent agreement between data and Monte Carlo
Source runs also provide energy calibration
Ge ZIP with 133Ba sourceIonization energy in keVIonization energy in keV
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Possible Sources of Beta Backgrounds
• Ejected betas from incident gammas. Monte Carlo of detector response and risetime analyses:
50% of our “beta contamination”, but less than 3% of our beta background 1 ejectron per 25k incident gammas appears in the nuclear recoil band
• Radon contamination on the copper cans or the detectors themselves. Alpha analyses (a:b ~ 1:1 for 210Pb) 30-60% of our background.
• K contamination introduced during fabrication & adventitious surface C Ion beam characterization 20-30% of the beta background.
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Expected Backgrounds
Source Expected # events (WIMP search Ge data set)
Cosmogenic punch-through neutrons
< 0.3 events (90% CL) given no veto-coincident neutrons
Beta leakageCuts applied to extra Cal. sets
0.67 events (90% CL)
Beta leakageCal. distribution extrapolation
0.88 +/- 0.45
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Blind Analysis of WIMP Search Data
Same Tower 1 as run at Stanford: 52.6 live days raw, 19.4 kg-d of Ge after cuts
All detector evaluations and cut definitions were done with calibration runs.Veto anti-coincident WIMP search data in the nuclear recoil region was blinded.
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Cuts applied to WIMP search data(all detectors summed)
CUTS Evts
Raw 968,680Data Quality 807,419Q and P thresh 199,338Veto anti-coinc194,088 Single scatters 87,596< 100 keV recoil
13,947Qinner electrode 8,845Pileup cut 8,240Timing cut 1,249N-recoil band 1
Raw Wimp Search Data
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
After applying Cuts: Wimp search data for individual detectors
Contaminated by calibration source
seen in previous shallow run
Saw no events in nuclear recoil band in Blind Search
But after unblinding,we found a software error: Fit for saturated pulses had been also applied to many unsaturated events.
Correction improves cut efficiency, but Z5 event now passes.
All plots shown are for corrected data.
Si
SiGe
Ge
Ge Ge
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Calculate limits
New Limit is 4 x better than Edelweiss
10 x better than CDMS I
Not consistent with WIMPs being the DAMA annual modulation signal
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
CDMS II Future Plans
Current data run (Mar 25th to Aug 9th, 2004) ~65 live days with 2 towers of detectors (5 Ge ZIPs)Charge thresholds lowered by ~20% (improved electronics grounding) More 133Ba calibration data to improve beta systematic analyses
New analysis methodsImproved Z-position reconstruction5-parameter phonon timing cut w/covariance matrixImprove timing resolution of phonon leading edge by pulse fitting
Warm up Aug-Oct, 2004 to install 5 towers of detectorCryocooler (already tested) to handle the added heat load
Run until Dec 2005 to achieve ~ x 20 increase in sensitivity
ICHEP Beijing, ChinaAugust 16-22, 2004
Professor Priscilla CushmanUniversity of Minnesota
Summary
• CDMS has successfully collected data at Soudan Finished the analysis of that first data run
results submitted to PRL: astro-ph/0405033
• No WIMP signal was observed. Current CDMS limits improve by a factor of ~4
(assuming standard DM halo and WIMP scalar interactions)
• No anticipated problems to achieving x 20 improvement