CDMS-II to SuperCDMS

Transcription

1 CDMS-II to SuperCDMS WIMP search at a zeptobarn Tobias Bruch University of Zürich 5 th Patras Workshop on Axions,WIMPs and WISPs University of Durham, 13 July 2009

2 CDMS-II 5 Tower setup 5 Towers a 6 detectors (Ge/Si) operated at cryogenic temperatures (~40 mk) Underground laboratory shields well against cosmic radiation Active veto for high energetic muons Passive shielding against environmental radioactivity 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 1

3 CDMS detectors Ionization Signal Phonon Signal 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 2

4 Primary background rejection Dominant backgrounds (γ, e ± ) produce electron recoils WIMPS and neutrons produce nuclear recoils Suppressed ionization signal for nuclear recoils Define ionization yield: 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 3

5 Yield based rejection Primary electron recoil rejection :1 Low yield surface event population remains. Signal region: 2σ nuclear recoil band Ionization suppression in good agreement with Lindhard theory 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 4

6 Backgrounds in CDMS-II Low yield surface events are the dominating background 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 5

7 Detector 2 energy [kev] Surface contaminations of the crystals Environmental 222 Rn deposits 210 Pb β source on the surface of the crystals Expected signature: Low energy β decay detect the ~46 kev peak Select decay by NND events Detector 1 energy [kev] 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 6

8 surface nearest-neighbor double scatters in 46 kev sum peak [/detector pair/day] Ionization Energy [MeV] Second signature of 210 Pb Bi 210 Po 206 Pb + α Select alphas from NND: low yield α + recoiling 206 Pb nucleus Recoil Energy [MeV] Correlation of 210 Pb surface NND and 210 Po α/recoiling 206 Pb strongly supports 210 Pb theory α/recoiling nucleus pairs [/detector pair/day] Build full surface event model to determine the β rate from 210 Pb contamination 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 7

9 Break down of numbers black = 10-3 counts/ detector/day blue = 10-3 counts/kg/ day (eff-corr.) Total, all towers Total, T12 Total, T Pb, all towers 210 Pb, T Pb, T Pb decays kev surface event singles 65 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 131 non- 210 Pb, all 23 ± 11 towers 131 ± 63 photon expected, 38 ± 18 all towers 217 ± 103 Old towers New towers Factor 2.5 ± 2.5 improvement 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 8

10 Break down of numbers black = 10-3 counts/ detector/day blue = 10-3 counts/kg/ day (eff-corr.) Total, all towers Total, T12 Total, T Pb, all towers 210 Pb, T Pb, T Pb decays kev surface event singles 65 ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± ± 131 non- 210 Pb, all 23 ± 11 towers 131 ± 63 photon expected, 38 ± 18 all towers 217 ± 103 Remanent β rate not associated with 210 Pb decays Photons can knock off electrons from materials Additional source of β events Rate can be measured from calibration data 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 9

11 Timing of phonon signals Delay Surface events are faster in timing than bulk nuclear recoils Risetime Timing is a powerful discriminator for surface events 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 10

12 Surface event rejection cut Defined on calibration data Applied to low background data Surface event rejection ~ 200:1 Cut set to allow ~0.5 events total leakage to WIMP candidates 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 11

13 Unblinding the signal region Use singles and multiples in the signal region to measure the expected leakage (stat.) -0.2 (syst.) No events observed in the 2σ NR band R123/124: 397 kg-d Ge exposure Likely α-induced NR Consistent with leakage outside the signal region 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 12

14 Recent results Spin-independent WIM WIMP!neutron! SD [cm 2 ] 10!44 10!36 10!37 10!38 10!39 Spin-dependent 10! WIMP mass [GeV/c 2 ] 6.6x10-44 cm 60 GeV 2.7x10-38 cm 60 GeV 4.6x10-44 cm 60 GeV 1.8x10-38 cm 60 GeV (combined with previous CDMS data) (combined with previous CDMS data) 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 13

15 Electromagnetic Dark Matter signatures? What if we miss a dark matter signal due to an electron recoil interaction? Ionization yield Energy [kev] Analysis motivated by the DAMA/LIBRA modulation signature. 5th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 14

16 Low energy spectrum Rate [cpd kg!1 kev!1 ] DAMA Energy = 3.15 ± 0.02 kev Width = ± kev Rate = ± cpd kg!1 Excess in detected rate in the DAMA low energy spectrum Contribution from 40 K (3.2 kev) unknown Energy [kev] Assumption: conversion of dark matter particle to electromagnetic energy No excess rate above background detected Rate [cpd kg!1 kev!1 ] CDMS-II likely 55 Mn Energy = 6.54 ± 0.1 kev Rate = 0.44 ± 0.09 cpd kg!1 Energy = 8.98 kev ( 65 Zn) Rate = 0.73 ± 0.1 cpd kg! Energy [kev] 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 15

17 Comparison with DAMA/LIBRA Rate [cpd kg!1 ] DAMA Rate [cpd kg!1 ] NaI Modulation Energy [kev] Ge Energy [kev] Z 2 scaling of the CDMS upper limits is an arbitrary toy model In need of an actual particle model to perform physical interpretation 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 16

18 5 Towers - the second part Second run with the 5 Tower setup since July 2007 Factor ~2.5 more exposure Improved data processing New phonon pulse information yielding possible discrimination potential Aim to keep expected backgrounds at the same (better lower) level as for the most recent analysis Analysis of the data is ongoing while we speak 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 17

19 Surface event discrimination T1Z5 calibration data 10 2 R Ba surface R Ba surface R Cf neutrons R Cf neutrons Counts !10! Timing discriminator [µ s] Timing for the new data looks promising in obtaining higher nuclear recoil detection efficiency 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 18

20 CDMS-II sensitivity till 2009 Raw Exposures R ~120 kgd R ~400 kgd R ~520 kgd R ~750 kgd Total of ~1300 kgd Final CDMS-II results expected in August 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 19

21 The dawn of a new age Veto ST1 T3 Mass x 2.54 Si Ge Improved active Al coverage better phonon collection Veto Final tuning of the first super tower last week ready for taking data 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 20

22 Improved timing information CDMS-II configuration ST-I configuration New phonon sensor configuration strongly improves the timing discrimination Detectors used in the next Stage of CDMS 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 21

23 CDMS-II to SuperCDMS 100kg August this year 5 Soudan ~2 year sensitivity SuperCDMS 100kg zeptobarn sensitivity 5 th Patras Workshop on Axions, WIMPs and WISPs, University of Durham, July 13, 2009 Tobias Bruch, University of Zürich 22

24 Summary Excellent knowledge of the backgrounds and discrimination make the CDMS-II experiment to a zero background experiment Latest CDMS-II results set an world leading 90%CL exclusion limit on the WIMP nucleon cross-section for masses > 42 GeV Started to look not only for standard dark matter interactions Final CDMS-II data has been taken and is currently under analysis with final results expected in August this year Successful development and integration of the first SuperTower used in the next stage of the CDMS experiment Continuos improvements of the CDMS collaboration in reaching the zeptobarn sensitivity

25 The CDMS-II Collaboration Caltech Z. Ahmed, J. Filippini, S. R. Golwala, D. Moore, R. W. Ogburn Case Western Reserve University D. S. Akerib, C. N. Bailey, K. Clark, M.R. Dragowsky, D. R. Grant, R. Hennings-Yeomans Fermilab D. A. Bauer, F. DeJongh, J. Hall, D. Holmgren, L. Hsu, E. Ramberg, J. Yoo MIT E. Figueroa-Feliciano, S. Hertel, S. Leman, K. McCarthy NIST K. Irwin Queens University W. Rau Santa Clara University B. A. Young Stanford University P.L. Brink, B. Cabrera, J. Cooley, M. Pyle, S. Yellin Syracuse University M. Kiveni, M. Kos, R.W. Schnee Texas A&M R. Mahapatra University of California, Berkeley M. Daal, N. Mirabolfathi, B. Sadoulet, D. Seitz, B. Serfass, K. Sundqvist University of California, Santa Barbara R. Bunker, D. O. Caldwell, H. Nelson, J. Sander University of Colorado at Denver M. E. Huber University of Florida T. Saab, D. Balakishiyeva University of Minnesota P. Cushman, L. Duong, M. Fritts, V. Mandic, X. Qiu, A. Reisetter, O. Kamaev University of Zurich S. Arrenberg, T. Bruch, L. Baudis

26 BACKUP SLIDES

27 Understanding the origin of our backgrounds

28 Backgrounds for the new data Gamma spectrum, T4 germanium ZIPs only Counts / (kg d kev) !1 238 [kev] 352 [kev] 511 [kev] 609 [kev] 911 [kev] 969 [kev] 1173 [kev] 60Co 1120 [kev] 1588 [kev] 228Ac [kev] DE 208Tl 1238 [kev] 1335 [kev] 60Co 1464 [kev] 40K 1765 [kev] 2204 [kev] 2448 [kev] R kgd R kgd R kgd R kgd R kgd 2615 [kev] 10!2 10! Energy [kev]

29 210 Pb decay scheme 210 Pb, 22 yr 63.6 kev BR 16+3% 210 Bi* <3 ns! kev 4.25±0.04% ToI 210 Bi kev, BR 84+3% M e kev 4.3±1.4% e kev 16±5% N e - 46 kev 0.9±0.3% e kev 57±2% L1 e kev 6.0±0.2% L2 e kev 0.50±0.02% Campbell, J. Phys. A 36, 3219 (2003) Literature Review Nucl. Data Tables A4, 1 (1968) Nucl. Data Tables A6, 235 (1969 Nucl. Data Tables A9, 119 (1971 Atom. Data. Nucl. Data Tables A81, 1, (2002). L3 24.6±0.8% emit Flourescent x-rays NOP Mostly Auger electron emission Expected signature: Low energy beta decay -> detect the ~46 kev peak H. Nelson