Cryogenic Dark Matter Search Results from the Cryogenic Dark Matter Search Wolfgang Rau On behalf of the CDMS collaboration

CDMS Collaboration CDMS resutls – W. Rau - SNOLAB Workshop 2010 California Institute of Technology Z. Ahmed, J. Filippini, S.R. Golwala, D. Moore Case Western Reserve University D. Akerib, C.N. Bailey, M.R. Dragowsky, D.R. Grant, R. Hennings-Yeomans Fermi National Accelerator Laboratory D. A. Bauer, F. DeJongh, J. Hall, D. Holmgren, L. Hsu, E. Ramberg, R.L. Schmitt, J. Yoo Massachusetts Institute of Technology E. Figueroa-Feliciano, S. Hertel, S.W. Leman, K.A. McCarthy, P. Wikus NIST * K. Irwin Queen’s University C. Crewdson *, P. Di Stefano *, J. Fox *, S. Liu *, C. Martinez *, P. Nadeau *, W. Rau Santa Clara University B. A. Young SLAC/KIPAC * M. Asai, A. Borgland, D. Brandt, W. Craddock, E. do Couto e Silva, G.G. Godrey, J. Hasi, M. Kelsey, C. J. Kenney, P. C. Kim, R. Partridge, R. Resch, J.G. Weisend, D. Wright Southern Methodist University J. Cooley Stanford University P.L. Brink, B. Cabrera, M. Cherry *, R. Moffatt*, L. Novak, R.W. Ogburn , M. Pyle, M. Razeti*, B. Shank*, A. Tomada, S. Yellin, J. Yen* Syracuse University M. Kos, M. Kiveni, R. W. Schnee Texas A&M K. Koch*, R. Mahapatra, M. Platt *, K. Prasad*, J. Snader University of California, Berkeley M. Daal, T. Doughty* , N. Mirabolfathi, A. Phipps, B. Sadoulet, D. Seitz, B. Serfass, D. Speller*, K.M. Sundqvist University of California, Santa Barbara R. Bunker, D.O. Caldwell, H. Nelson University of Colorado Denver B.A. Hines, M.E. Huber University of Florida T. Saab, D. Balakishiyeva, B. Welliver * University of Minnesota H. Chagani*, J. Beaty, P. Cushman, S. Fallows, M. Fritts, T. Hoffer*, O. Kamaev, V. Mandic, X. Qiu, R. Radpour*, A. Reisetter, A. Villano*, J. Zhang University of Zurich S. Arrenberg, T. Bruch, L. Baudis, M. Tarka * new collaborators or new institutions in SuperCDMS

Overview Introduction – Dark Matter CDMS technology CDMS resutls – W. Rau - SNOLAB Workshop 2010 Overview Introduction – Dark Matter CDMS technology Data Analysis and WIMP Results Other Results (time permitting)

Introduction – Dark Matter CDMS resutls – W. Rau - SNOLAB Workshop 2010 Introduction – Dark Matter Coma Cluster Zwicky, 1930s Coma cluster Dark Matter CDMS Technology Strong and multiple observational evidence for dark matter Weakly Interacting Massive Particles (WIMPs) are among the best motivated candidates. Vera Rubin-Cooper, Rotation curves 1970s Analysis Results Other Analyses Abell 2218 (HST) Gravitational Lensing Bullet Cluster Conclusion WMAP

Ionization energy [keV eeq] CDMS resutls – W. Rau - SNOLAB Workshop 2010 CDMS Technology Operating Principle Phonon signal: measures energy deposition Ionization signal: distinguishes between electron (large) and nuclear recoils (small) Surface events have reduced ionization: need additional information to identify Thermal coupling Thermal bath Dark Matter Evidence Phonon sensor + - Target CDMS Technology e n Analysis Results Other Analyses Ionization energy [keV eeq] Phonon signal Electron recoils from β’s and γ’s Conclusion Electron recoil Nuclear recoil Charge signal Nuclear recoils from neutrons Phonon energy [keV]

CDMS Technology Detectors Cryogenic ionization detectors, Ge (Si) CDMS resutls – W. Rau - SNOLAB Workshop 2010 CDMS Technology Detectors Cryogenic ionization detectors, Ge (Si)  = 7 cm, h = 1 cm, m = 250 g (100 g) Thermal readout: superconducting phase transition sensor (TES) Transition temperature: 50 – 100 mK 4 sensors/detector, fast signal (< ms) Charge readout: Al electrode, divided Dark Matter Evidence CDMS Technology Analysis Results Other Analyses Conclusion

CDMS Technology Surface effect + E Detector Performance Detector CDMS resutls – W. Rau - SNOLAB Workshop 2010 CDMS Technology Detector Performance Detector Collimator Dark Matter g-band n-band Evidence CDMS Technology Ionization/Recoil energy b-band Analysis Results Recoil energy [keV] Other Analyses gs neutrons bs surface event nuclear recoil rising edge slope Surface effect Conclusion + + – + – E Reduced charge signal but faster phonon signal

CDMS Technology Experimental Setup „Tower“ Soudan (6 Detectors) CDMS resutls – W. Rau - SNOLAB Workshop 2010 CDMS Technology Experimental Setup „Tower“ (6 Detectors) Soudan Underground lab (2000 m w.e.) Dark Matter Evidence CDMS Technology Analysis Results Cryostat, Coldbox Shielding Other Analyses Conclusion 5 Towers (~ 5 kg Ge ) operated 2006 – 2008

Data Analysis Event Reconstruction Event reconstruction CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Event Reconstruction Event reconstruction For each trigger ALL detectors are read out, including muon-veto Optimal Filter (phonon pulse shape varying, so not really ‘optimal’, but gives best resolution) Extract basic parameters (Amplitude, Event time) Multi-parameter pulse fit Events time-stamped to correlate with slow control parameters / Minos neutrino beam Dark Matter Evidence Time bins [0.8 s] Amplitude [a.u.] CDMS Technology Analysis Results Other Analyses Conclusion

Data Analysis Data Quality Kolmogorov-Smirnov test CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Data Quality Kolmogorov-Smirnov test Pick a few ‘golden’ data sets Compare parameter distributions Dark Matter Evidence Example Detector neutralization / low yield events CDMS Technology Charge carriers trapped at defects  build up counter field  poor charge collections  increase background datasets templates Analysis Results Fraction of low yield events Date Other Analyses average 5 above average (colored points = poorly neutralized datasets) Conclusion

Data Analysis Data Quantity Total raw exposure is 612 kg-days CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Data Quantity Dark Matter Evidence recorded data Total raw exposure is 612 kg-days CDMS Technology some detectors not analyzed for WIMP scatters Analysis Results raw exposure periods of poor data quality removed Other Analyses this work Conclusion 2008 published data

Data Analysis Position Dependent Calibration CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Position Dependent Calibration Large area sensor not completely homogeneous Use extensive  calibration to create lookup table for position dependent pulse height/timing distributions Compare each event from WIMP search data with  events at same location Position determination not perfect: ambiguity close to edge of detector where timing distributions are changing quickly May lead to miscalibration Dark Matter Position Dependence of Timing Parameter (measured with e-recoils) Evidence CDMS Technology events near and outside fiducial volume Analysis Results Radius from arrival time Timing parameter increasing radius Other Analyses Conclusion Radius from energy partition Improvement in this analysis Include s outside fiducial volume in lookup table  reduces timing outliers from miscalibration

Background Estimate – Neutrons CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Background Estimate – Neutrons Dark Matter Radiogenic Neutrons From rock negligible (neutron shield!) From experimental setup estimated from screening measurements,  BG analysis Main contributions from spontaneous fission of U in Cu/Pb Caveat: cannot measure U with  screening, only daughters – ICPMS measurement for EXO (Pb from same source) indicate lower contamination Total 0.03 – 0.06 events expected Cosmogenic Neutrons Muons in experimental setup; internal negligible (muon veto detector) Muons in surrounding rock; external Use Monte Carlo to estimate rate Compare MC for n from vetoed (internal) muons to measured rate Scale MC result for external muons by ‘measured/MC’ ratio for internal muons Expected rate: 0.04 (stat) Evidence CDMS Technology Analysis Results Other Analyses Conclusion + 0.04 – 0.03

Data Analysis Background Estimate – Surface Events, ‘Leakage’ CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Background Estimate – Surface Events, ‘Leakage’ Dark Matter Timing Distribution – Surface vs. Neutrons Evidence CDMS Technology Analysis Results Nuclear recoils from Cf neutron source Other Analyses Surface events from Ba calibration Conclusion Tail distribution different for each detector determines cut position

Data Analysis Background Estimate – Surface Events, ‘Leakage’ CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Background Estimate – Surface Events, ‘Leakage’ Look at surface events outside signal region (‘sideband’) Count events passing / failing cut – extrapolate to signal region Dark Matter Evidence Sideband 1 Multiple-scatters in NR band Sideband 2 Singles and multiples just outside NR band Sideband 3 Singles and multiples Ba calibration in wide region CDMS Technology Correct for systematic effects due to different distributions in energy and yield Analysis Results WIMP Search Data 133Ba 252Cf Other Analyses Conclusion Leakage estimate = ------------------------------ x # signal region, failing # sideband, passing # sideband, failing Estimates consistent; total expected leakage from ‘blind’ data: 0.6  0.1

Data Analysis Expected Sensitivity CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Expected Sensitivity Dark Matter Evidence CDMS Technology Analysis Results Other Analyses Conclusion

Data Analysis Unblinding signal region Failing Cut ( Surface events) CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Unblinding Dark Matter Evidence masked signal region (2 NR band) CDMS Technology 2 events near NR band Event 1: Tower 1, ZIP 5 (T1Z5) Sat. Oct. 27, 2007 8:48pm CDT Analysis Results signal region Other Analyses Conclusion Event 2: Tower 3, ZIP 4 (T3Z4) Sun. Aug. 5, 2007 2:41 pm CDT Failing Cut ( Surface events) Passing Cut ( Good events)

Post-unblinding Studies – Data Quality Recheck CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Post-unblinding Studies – Data Quality Recheck Dark Matter Evidence CDMS Technology Analysis Results Other Analyses Conclusion Everything seems to have been in best order

pulse height (ADC units) CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Post-unblinding Studies – Event Reconstruction Could there be a problem with the start time of the charge pulse? Closeup of template fit to ionization pulse for event 2 [ADC bin] pulse height (ADC units) Dark Matter Evidence CDMS Technology fitted start time What is the true start time? 2 of the fit template start time [ADC bin] Analysis Results Other Analyses affects only ~1% of events with <6 keV ionization energy mostly accounted for in the pre-unblinding leakage estimate. ~ Conclusion A more careful accounting revised the surface event leakage estimate from 0.6 to 0.8 events

Data Analysis Cut Variation and Probabilities CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Cut Variation and Probabilities Dark Matter Evidence Tightening cut to ~1/2 expected leakage would remove both events Would cost 26 % of exposure Loosening cut to ~2 expected leakage would add one more event Limit not very sensitive to cut position CDMS Technology Analysis Results Other Analyses 1.0 10 estimated surface event leakage from 133Ba Conclusion Probability to see 2 or more events from surface event leakage: ~20 % Probability to see 2 or more events from background including neutrons: ~23 % These values indicate that the results of this analysis cannot be interpreted as significant evidence for WIMP interactions, but we cannot reject either event as signal.

Data Analysis Likelihood analysis CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Likelihood analysis Determine how well the event distribution fits surface event hypothesis Compare to how well it fits nuclear recoil hypothesis Conclusion: either might be possible Dark Matter Evidence CDMS Technology Analysis Results Other Analyses Nuclear recoils from Cf neutron source Conclusion Surface events from Ba calibration

Data Analysis Limits Minimum @ ~70 GeV CDMS new 7.0  10-8 pb CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Limits Dark Matter Evidence CRESST 08 CDMS Technology CDMS (08) CDMS, new CDMS, total XENON 10 Expected sensitivity WARP Analysis Results EDELWEISS (09) ZEPLIN III Other Analyses Conclusion Minimum @ ~70 GeV CDMS new 7.0  10-8 pb CDMS combined 3.8  10-8 pb

Spin Dependent Interaction CDMS resutls – W. Rau - SNOLAB Workshop 2010 Spin Dependent Interaction PICASSO, COUPP, XENON Dark Matter Evidence CRESST I CDMS (n) XENON (n) XENON (p) KIMS (p) CDMS (p) KIMS (n) Interaction may depend on spin of target May also depend on spin carrying nucleon (p or n) DAMA could avoid conflict with CDMS and XENON COUPP and PICASSO exclude most of the DAMA region If nucleon type is ignored, XENON provides strong limit COUPP (p) CDMS Technology COUPP, 4 kg (p, prelim 2010) PICASSO (p) DAMA (p) Analysis Results SuperKamiokande (p) Other Analyses IceCube (p) Conclusion

Data Analysis Inelastic Dark Matter CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Inelastic Dark Matter Dark Matter Evidence Proposed by Wiener et al. could explain DAMA/LIBRA Scattering includes transition of WIMP to excited state ( E= ) DAMA allowed: marginalized over cross section Hashed: excluded at 90 % C.L. New (preliminary) results from CRESST: all DAMA allowed region excluded CDMS Technology Analysis Results Other Analyses Conclusion

CoGeNT – Evidence for Dark Matter? CDMS resutls – W. Rau - SNOLAB Workshop 2010 Other Results CoGeNT – Evidence for Dark Matter? Low threshold high resolution Ge detector Ultra low background No discrimination Observe rise in spectrum at low energy 2/dof for ‘no WIMP’ hypothesis: 20.4/20 Claim that fit with WIMPs is better (give example for fit with 2/dof = 20.1/18) Show preferred region Tension with CDMS Si data (PhD thesis by J. Filippini, no paper published yet) Dark Matter Evidence CDMS Technology Preliminary!! Analysis Results Other Analyses Conclusion

XENON100 – Preliminary Limit CDMS resutls – W. Rau - SNOLAB Workshop 2010 Other Results XENON100 – Preliminary Limit Dark Matter Evidence CRESST 08 CDMS Technology CDMS (08) XENON 100 CDMS, new CDMS, total XENON 10 WARP Analysis Results EDELWEISS (09) ZEPLIN III Other Analyses Conclusion

Other Analyses Axions Solar Axions CDMS resutls – W. Rau - SNOLAB Workshop 2010 Other Analyses Axions Solar Axions Convert in nuclear electric field to  “Bragg” condition enhances x-section Dark Matter Evidence CDMS Technology Analysis Results Other Analyses Conclusion

Low Energy Electron Recoils Spectrum CDMS resutls – W. Rau - SNOLAB Workshop 2010 Other Analyses Low Energy Electron Recoils Spectrum No excess above background! Interpretation with respect to relic axions: Signal: peak at axion mass No preferred direction Consider all electron recoil events Dark Matter Evidence CDMS Technology Analysis Results Other Analyses Conclusion

Ongoing Analyses Low Energy Threshold CDMS resutls – W. Rau - SNOLAB Workshop 2010 Ongoing Analyses Low Energy Threshold Dark Matter Evidence Expand energy range down to O(1 keV) No ER vs NR discrimination  will have background, but expected rate increases strongly at low energy (low mass WIMPs) Dedicated ultra-low threshold experiment employ Neganov-Luke effect (thermal signal amplification from drifting charges) Finalise Si analysis CDMS Technology Analysis Results Other Analyses Conclusion

CDMS resutls – W. Rau - SNOLAB Workshop 2010 Conclusion Dark Matter CDMS Technology We present the analysis of new data comprising 612 kgd raw exposure Expected background is 0.8 from surface events and <0.1 from neutrons We observe 2 events This result is statistically compatible with expected background (23 % prob), so they do not constitute statistically significant signal Both events are compatible with being nuclear recoils or surface event background Other analyses: solar axions, low energy ER, low threshold WIMP analysis Analysis Results Other Analyses Conclusion

Fine CDMS resutls – W. Rau - SNOLAB Workshop 2010 Cryogenic Evidence Super- heated Scintillator Directional Conclusion