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Results from the Cryogenic Dark Matter Search

Results from the Cryogenic Dark Matter Search. Wolfgang Rau On behalf of the CDMS collaboration. CDMS Collaboration. California Institute of Technology Z. Ahmed, J. Filippini , S.R. Golwala , D. Moore

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Results from the Cryogenic Dark Matter Search

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

  2. CDMS resutls – W. Rau - SNOLAB Workshop 2010 CDMS Collaboration California Institute of TechnologyZ. Ahmed, J. Filippini, S.R. Golwala, D. Moore Case Western Reserve UniversityD. Akerib, C.N. Bailey, M.R. Dragowsky, D.R. Grant, R. Hennings-Yeomans Fermi National Accelerator LaboratoryD. A. Bauer, F. DeJongh, J. Hall, D. Holmgren, L. Hsu, E. Ramberg, R.L. Schmitt, J. Yoo Massachusetts Institute of TechnologyE. Figueroa-Feliciano, S. Hertel, S.W. Leman, K.A. McCarthy, P. Wikus NIST *K. Irwin Queen’s UniversityC. Crewdson*, P. Di Stefano *, J. Fox *, S. Liu *, C. Martinez *, P. Nadeau *, W. Rau Santa Clara UniversityB. 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 UniversityJ. 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 UniversityM. Kos, M. Kiveni, R. W. Schnee Texas A&MK. 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 BarbaraR. Bunker, D.O. Caldwell, H. Nelson University of Colorado DenverB.A. Hines, M.E. Huber University of FloridaT. 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 ZurichS. Arrenberg, T. Bruch, L. Baudis, M. Tarka * new collaborators or new institutions in SuperCDMS

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

  4. CDMS resutls – W. Rau - SNOLAB Workshop 2010 Abell 2218 (HST) Coma Cluster Introduction – Dark Matter 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 WMAP Other Analyses Conclusion Gravitational Lensing Bullet Cluster

  5. CDMS resutls – W. Rau - SNOLAB Workshop 2010 Thermal bath Thermal coupling Phonon sensor e n + + + - - Target - Ionization energy [keVeeq] - + + - - + + - + + + + Phonon energy [keV] - - - - 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 Dark Matter Evidence CDMS Technology Analysis Results Other Analyses Electron recoils from β’s and γ’s Phonon signal Conclusion Electron recoil Nuclear recoil Charge signal Nuclear recoils from neutrons

  6. 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

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

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

  9. 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 CDMS Technology Analysis Results Amplitude [a.u.] Other Analyses Conclusion Time bins [0.8 s]

  10. 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 Fraction of low yield events Analysis Results Date Other Analyses average 5 above average (colored points = poorly neutralized datasets) Conclusion datasets templates

  11. 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 periods of poor data quality removed raw exposure Other Analyses this work Conclusion 2008 published data

  12. 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

  13. CDMS resutls – W. Rau - SNOLAB Workshop 2010 Data Analysis Background Estimate – Neutrons Dark Matter Evidence • 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) CDMS Technology Analysis Results Other Analyses Conclusion + 0.04 – 0.03

  14. 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

  15. 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 CDMS Technology Sideband 1 Multiple-scatters in NR band Sideband 2 Singles and multiples just outside NR band Sideband 3 Singles and multiples Bacalibration in wide region Analysis Results • 133Ba • 252Cf WIMP Search Data Correct for systematic effects due to different distributions in energy and yield Other Analyses Conclusion # sideband, passing # sideband, failing Leakage estimate = ------------------------------ x # signal region, failing Estimates consistent; total expected leakage from ‘blind’ data: 0.6  0.1

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

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

  18. 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

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

  20. 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.

  21. 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

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

  23. CDMS resutls – W. Rau - SNOLAB Workshop 2010 Spin Dependent Interaction PICASSO, COUPP, XENON Dark Matter Evidence • 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 KIMS (n) CDMS Technology COUPP (p) CDMS (p) CRESST I DAMA (p) Analysis Results COUPP, 4 kg(p, prelim 2010) PICASSO (p) KIMS (p) CDMS (n) Other Analyses XENON (n) SuperKamiokande (p) Conclusion XENON (p) IceCube (p)

  24. 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

  25. 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

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

  27. 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

  28. 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

  29. CDMS resutls – W. Rau - SNOLAB Workshop 2010 Ongoing Analyses Low Energy Threshold Dark Matter Evidence CDMS Technology • 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 experimentemploy Neganov-Luke effect (thermal signal amplification from drifting charges) • Finalise Si analysis Analysis Results Other Analyses Conclusion

  30. 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

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

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