Recent Results from the Cryogenic Dark Matter Search Bruno Serfass - UC Berkeley on behalf of the CDMS and SuperCDMS collaborations
CDMS/SuperCDMS Collaborations DOE NSF California Institute of Technology Z. Ahmed, J. Filippini, S.R. Golwala, D. Moore 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. Crewdon*, P. Di Stefano*, O. Kamaev, C. Martinez*, K.Page*, P. Nadeau*, W. Rau, Y. Ricci* Saint Olaf College A. Reisetter Santa Clara University B. A. Young SLAC National Accelerator Laboratory/KIPAC* M. Asai*, A. Borgland*, D. Brandt*, P.L. Brink, W. Craddock*, E. do Couto e Silva*, G. Godfrey*, J. Hasi*, M. Kelsey*, C. J. Kenney*, P. C. Kim*, R. Partridge*, R. Resch*, K. Schneck*, A. Tomada, D. Wright* Southern Methodist University J. Cooley, B. Karabuga, H. Qiu * new collaborators or new ins/tu/ons in SuperCDMS Stanford University B. Cabrera, M. Cherry, L. Novak, R.W. Ogburn, M. Pyle, M. Razeti*, B. Shank*, S. Yellin, J. Yen* Syracuse University R. Bunker, Y. Chen*, M. Kiveni, M. Kos, R. W. Schnee Texas A&M K. Koch*, R. Mahapatra, M. Platt*, K. Prasad*, J. Sander 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 D.O. Caldwell, H. Nelson University of Colorado Denver B.A. Hines, M.E. Huber University of Florida T. Saab, D. Balakishiyeva, B. Welliver * FT-UAM/CSIC and Universidad Autonoma de Madrid* D. G. Cerdeño*, L. Esteban* University of Minnesota H. Chagani*, J. Beaty, P. Cushman, S. Fallows, M. Fritts, T Hofer*, O. Kamaev, V. Mandic, X. Qiu, R. Radpour*, A. Villano*, J. Zhang 2
CDMSII Detectors 250g Ge or 100g Si 1cm thick x 7.5 cm diameter Phonon sensors on one face 4 quadrant with 888 TES sensor each Can lower thresholds significantly 4 R (Ω) 3 2 1 ~ 10mK T c ~ 80mK T (mk) 1 µ tungsten 380µ x 60µ aluminum fins Charge readout on the other face divided into inner fiducial volume and outer guard ring measure ionization in low E field (~ volts/cm) 2.0 kev nuclear recoil phonon pulse, T1Z5 3
CDMSII at Soudan Data taken with 5 Towers (30 detectors) between Oct. 2006 to Sept. 2008 WIMP search 10-100keV recoil published in 2010 (Ge detector): Ahmed et al., Science 327:1619-1621,2010 2 candidate events observed σ 3.8 x 10-44 cm 2 (90% C.L) @WIMP mass 70 GeV/c 2 Combined Limits from CDMS-Edelweiss (PRD 84, 011102(R) (2011)) On-going reanalysis using improved algorithms, include Si detectors Low Threshold (2 kev nr ) Analysis published in 2011 Ahmed et al., PRL 106, 131302 (2011); arxiv:1011.2482 (w/ addional commentary) Use 8 detectors with lowest trigger thresholds Small subset (1/4 of the data) used to study backgrounds at low energy Background limited: No phonon-timing cut since ineffective below ~5 kev, ionization yield is less effective 4
Low Threshold Analysis: Energy Calibration Phonon energy scale calibrated with electron recoil lines at 1.3 kev and 10.37 kev Nuclear recoil energy reconstructed from phonon signal alone after subtracting Neganov-Luke phonons (~15% of signal at low E) Start by assuming same scale as for electron recoils Measure mean ionization yield as function of inferred recoil energy for calibration neutrons down to 4 kev nr, power-law extrapolation to lower energies Electron recoil phonon spectrum, T1Z5 10.39±0.022 kevee Ionization Yield = Phonon-based recoil energy 1.333±0.025 kevee Lindhard (k=0.157) CDMS
Low Threshold Analysis: WIMP candidate selection Nuclear recoil acceptance region defined as (+1.25,-0.5)σ band in ionization energy Maximizes sensitivity to nuclear recoils while minimizing expected backgrounds Neutron calibration T1Z5 detector 6
Low Threshold Analysis: WIMP candidate selection Nuclear recoil acceptance region defined as (+1.25,-0.5)σ band in ionization energy Maximizes sensitivity to nuclear recoils while minimizing expected backgrounds T1Z5 detector 7
Low Threshold Analysis: WIMP candidate selection Nuclear recoil acceptance region defined as (+1.25,-0.5)σ band in ionization energy Maximizes sensitivity to nuclear recoils while minimizing expected backgrounds 1.3 kev line Compton Surface Zero-charge 8
Low WIMP Mass Limits Conservatively assume all candidates could be from WIMP NO background subtraction! Limits set using optimum interval method: S. Yellin, PRD, 66, 032005 (2002); arxiv:0709.2701v1 (2007) CDMS SUF (1 kev thresh) CDMS Soudan (10 kev thresh) DAMA/LIBRA For spin-independent, elastic scattering, 90% CL limits incompatible with DAMA/LIBRA and CoGeNT excess CDMS Low Threshold CoGeNT XENON10 XENON100 CDMS all det CoGeNT, L-shell peaks and constant bkgnd removed CDMS T1Z5 Ahmed et al., PRL 106, 131302 (2011); arxiv:1011.2482 Note: CoGeNT region not updated for revision to surface event contamination m χ =7 GeV/c 2 (90% CL) σ SI ~7x10-41 2x10-40 cm 2 Hooper et al., PRD 82 123509 (2010) If only a small fraction of the low-energy excess events in CoGeNT are due to WIMPs, then constraints from CDMS II can be avoided 9
Search for Annual Modulation CDMS II data nearly two annual cycles, from Oct. 2006 to Sept. 2008 Data quality and detector selection criteria in this analysis are identical to low threshold analysis Nuclear recoil acceptance region defined as ±2σ band in ionization energy to increase sensitivity We consider 3 energy intervals between 5 and 11.9 kev nr : [5,7.3], [7.3,9.6], and [9.6,11.9] kev nr For nuclear recoils, the electron recoil equivalent energy measured by CoGeNT would be [1.2,1.8], [1.8,2.5], and [2.5,3.2] kev ee 5 kev nr threshold high enough to have a nearly 100% trigger efficiency 11.9 kev nr maximum energy to match the highest energy of CoGeNT For electron recoils with the same total phonon, the equivalent E rang would be [3,4.4], [4.4,5.9], and [5.9,7.4] kev ee 10
Search for Annual Modulation What effect are we trying to test? In the lowest energy bin, [5, 7.3] kev nr, the nuclear-recoil rate measured for CDMS is 0.29 [kev nr kg day] -1 Maximum likelihood estimate for the CoGeNT modulation amplitude is 0.35±0.015 [kev nr kg day] -1 Would require modulation fraction in CDMS of nearly 100% (same for full energy range) 11
Stability Cut Efficiencies Test stability nuclear-recoil band and charge fiducial ( Qinner ) cut efficiencies using calibration data Using Feldman-Cousins method, determine confidence limits on the amplitude and phase of annual modulation Qinner NR band Averages run-by-run Contours: 68%, 95%, 99% Nuclear-recoil cut: efficiency modulation upper limit of 1.2% at 90% confidence level Qinner cut: efficiency modulation upper limit 2.3 % at 90% confidence level Consistent with no modulation (similar constraints for all energy bins) 12
Results: Nuclear Recoil Singles No significant evidence for annual modulation In the energy range [5, 11.9] kev nr, all modulated rate with amplitudes greater than 0.07 [kev nr kg day] -1 are ruled out with a 99% confidence. Annual modulation signal of CDMS and CoGeNT are incompatible at >95% C.L. (preliminary) for the full energy range (if CoGeNT signal originates in a nuclear-recoil population) CoGeNT PRELIMINARY CDMS PRELIMINARY Contours: 68%, 95%, 99% 13
Results: Nuclear Recoil Singles No significant evidence for annual modulation In the energy range [5, 11.9] kev nr, all modulated rate with amplitudes greater than 0.07 [kev nr kg day] -1 are ruled out with a 99% confidence. Annual modulation signal of CDMS and CoGeNT are incompatible at >95% C.L. (preliminary) for the full energy range (if CoGeNT signal originates in a nuclear-recoil population) CDMS CoGeNT CoGeNT PRELIMINARY CDMS PRELIMINARY Contours: 68%, 95%, 99% 14
Results: Electron-recoil-dominated Singles/Multiples Data sample with no ionization-yield cut No significant evidence for annual modulation for both singles and multiples Little overlap with the energy range of CoGeNT under the hypothesis of an ER modulation. (3.2 kevee max for CoGeNT) This result cannot exclude the possibility that the modulation observed by CoGeNT is due to electron-recoils. PRELIMINARY Singles Singles Multiples Contours: 68%, 95%, 99% PRELIMINARY PRELIMINARY Multiples 15
Conclusion Both CDMS and CoGeNT use Ge target: model-independent check of whether the reported CoGeNT modulating signal is due to (standard) WIMPs No significant evidence for annual modulation for nuclear recoils between 5-11.9 kev nr Annual modulation signal of CDMS and CoGeNT are incompatible at >95% C.L. for the full energy range No significant evidence for annual modulation for electron-recoil dominated sample in the same energy range (corresponding to 3 7.4 kev ee ), however little overlap with the energy range of CoGeNT A paper will be put on the archives in the coming few days SuperCDMS soon ready to take physics data! 15 larger (1 inch) detectors with double sided phonon-charge sensors installed in Soudan Detector commissioning on-going More in Enectali Figueroa-Feliciano s talk (Fri 11:10am)! 16
Extra slides
NR scale
Electron Recoil Background 1.3 kev line Compton Surface 2σ zero charge band Zerocharge
Limits without T1Z5 After removing T1Z5, the limits are ~30% worse at 8 GeV
Zero Charge Events Zero charge events seen in WIMP search singles, WIMP search multiples, and Ba calibration data with similar spectra
CDMS II exposure
Stability Cut Efficiencies Qinner NR band
Results: Nuclear Recoil Singles
Results: Electron-recoil-dominated Singles/Multiples