Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 First Results from the Cryogenic Dark Matter Search at the Soudan Underground Laboratory Priscilla Cushman University of Minnesota

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 Composition of the Cosmos WIMPs WMAP best fit

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 Moving from a Shallow Site at Stanford to a Deeper Site at the Soudan Underground Mine in Northern Minnesota 1 per minute in 4 m 2 shield Depth (mwe) Log 10 (Muon Flux) (m -2 s -1 ) Stanford Underground Site 500 Hz muons in 4 m 2 shield Depth 713 m (2090 mwe) Reduce neutron background from ~1 / kg / day to ~1 / kg / year Reduce cosmic muon flux by ~ 30,000

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 Brown University M. Attisha, R.J. Gaitskell, J.P. Thomson, Case Western Reserve University D.S. Akerib, M. Dragowski, S. Kamat, R.W. Schnee, G.Wang Fermi National Accelerator Laboratory D. Bauer, M.B. Crisler, D. Holmgren, E. Ramberg Lawrence Berkeley National Laboratory J.H. Emes, A. Smith University of Florida L. Baudis Santa Clara University B.A. Young University of Minnesota, Minneapolis L. Duong, P. Cushman, A. Reisetter Stanford University P.L. Brink, B. Cabrera, C.Chang,R.W. Ogburn University of California, Berkeley V. Mandic, P. Meunier, N. Mirobalfathi, B. Sadoulet, D. Seitz, B. Serfass, K. Sundqujst University of California, Santa Barbara R. Bunker, D. O. Caldwell, R. Mahapatra, H. Nelson, J. Sander, S. Yellin. University of Colorado at Denver M. E. Huber The CDMS Collaboration …in the mine

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 The Soudan Underground Laboratory MINOS CDMS II Old: Soudan2 proton decay calorimeter New: Screening and Prototyping Area Applications welcome, see Operated by the University of Minnesota, in cooperation with Fermi National Accelerator Laboratory and the Minnesota Department of Natural Resources

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 CDMS II Facilities Mezzanine Main floor Electronics room Clean Room Loft Offices MINOS staging Detector Prep Clean room Mac hine Shop Main floor Mezzanine

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 CDMS Icebox and Shield plastic scintillators polyethylene lead ancient lead inner polyethylene Dilution Fridge | m |

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 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 crystal 1 cm thick x 7.5 cm diameter

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 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

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 Discrimination of nuclear recoils to electron recoils Yield = Ionization Energy Total Recoil Energy Calibration Data Surface betas are electron recoils with reduced charge collection

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 Timing provides further discrimination Use phonon risetime n-recoil is slower than e-recoil And Charge to phonon delay smaller for surface e’s gammas neutrons Ejectrons=e- products of incident radiation

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 Phonon energy in keV Excellent agreement between data and Monte Carlo Source runs also provide energy calibration Ge ZIP with 133 Ba source Ionization energy in keV

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 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 210 Pb)  30-60% of our background. K contamination introduced during fabrication & adventitious surface C Ion beam characterization  20-30% of the beta background.

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 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 leakage Cuts applied to extra Cal. sets 0.67 events (90% CL) Beta leakage Cal. distribution extrapolation /- 0.45

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 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.

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 Cuts applied to WIMP search data (all detectors summed) CUTSEvts Raw968,680 Data Quality807,419 Q and P thresh199,338 Veto anti-coinc194,088 Single scatters 87,596 < 100 keV recoil 13,947 Q inner electrode 8,845 Pileup cut 8,240 Timing cut 1,249 N-recoil band 1 Raw Wimp Search Data

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 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 Ge

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 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

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 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 133 Ba calibration data to improve beta systematic analyses New analysis methods Improved Z-position reconstruction 5-parameter phonon timing cut w/covariance matrix Improve timing resolution of phonon leading edge by pulse fitting Warm up Aug-Oct, 2004 to install 5 towers of detector Cryocooler (already tested) to handle the added heat load Run until Dec 2005 to achieve ~ x 20 increase in sensitivity

Professor Priscilla Cushman University of Minnesota ICHEP Beijing, China August 16-22, 2004 Summary CDMS has successfully collected data at Soudan Finished the analysis of that first data run results submitted to PRL: astro-ph/ 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