First Results from the Cryogenic Dark Matter Search at the Soudan Underground Laboratory

1. First Results from the Cryogenic Dark Matter Search at the Soudan Underground Laboratory Priscilla CushmanUniversity of Minnesota

2. Composition of the Cosmos WMAP best fit WIMPs

3. Moving from a Shallow Site at Stanford to a Deeper Site at the Soudan Underground Mine in Northern Minnesota Reduce neutron background from ~1 / kg / day to ~1 / kg / year Reduce cosmic muon flux by ~ 30,000 Depth 713 m (2090 mwe) 500 Hz muons in 4 m2 shield Stanford Underground Site Log10(Muon Flux) (m-2s-1) 1 per minute in 4 m2 shield Depth (mwe)

4. The CDMS Collaboration …in the mine • 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

5. The Soudan Underground Laboratory Operated by the University of Minnesota, in cooperation with Fermi National Accelerator Laboratory and the Minnesota Department of Natural Resources MINOS CDMS II Old: Soudan2 proton decay calorimeterNew: Screening and Prototyping Area Applications welcome, see http://www.hep.umn.edu/~prisca/soudan

6. CDMS II Facilities Electronics room Clean Room Loft Offices Main floor Detector Prep MINOS staging Cleanroom Machine Shop Mezzanine Mezzanine Main floor

7. CDMS Icebox and Shield plastic scintillators Dilution Fridge polyethylene lead ancient lead inner polyethylene |------------------ 2.18 m --------------------------|

8. ZIP Detectors and Tower Construction 250 g Ge or 100 g Si crystal 1 cm thick x 7.5 cm diameter 4 Phonon Channels: XY position Z position using timing and signal shape 2 Charge Channels: radial position

9. 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 Si ZIP Ge ZIP (very good signal/noise for a 20 keV true recoil energy event)

10. Discrimination of nuclear recoils to electron recoils Calibration Data Yield = Ionization Energy Total Recoil Energy Surface betas are electron recoils with reduced charge collection

11. Timing provides further discrimination Use phonon risetimen-recoil is slower than e-recoil And Charge to phonon delay smaller for surface e’s neutrons gammas Ejectrons=e- products of incident radiation

12. Source runs also provide energy calibrationGe ZIP with 133Ba source Ionization energy in keV Phonon energy in keV Excellent agreement between data and Monte Carlo

13. 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.

14. Expected Backgrounds

15. Blind Analysis of WIMP Search Data All detector evaluations and cut definitions were done with calibration runs. Veto anti-coincident WIMP search data in the nuclear recoil region was blinded. Same Tower 1 as run at Stanford: 52.6 live days raw, 19.4 kg-d of Ge after cuts

16. Cuts applied to WIMP search data(all detectors summed) Raw Wimp Search Data CUTS Evts Raw 968,680 Data Quality 807,419 Q and P thresh 199,338 Veto anti-coinc 194,088 Single scatters 87,596 < 100 keV recoil 13,947 Qinner electrode 8,845 Pileup cut 8,240 Timing cut 1,249 N-recoil band 1

17. After applying Cuts: Wimp search data for individual detectors Ge Ge 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 Contaminated by calibration source seen in previous shallow run Si Ge

18. Calculate limits New Limit is4 x better than Edelweiss 10 x better than CDMS I Not consistent with WIMPs being the DAMA annual modulation signal

19. 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 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

20. 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