Results from the CDMS Experiment Jodi Cooley Stanford University - PowerPoint PPT Presentation

Results from the CDMS Experiment Jodi Cooley Stanford University CDMS Analysis Coordinator TAUP 09 Jodi Cooley - Stanford University 1

CDMS II Collaboration Caltech Syracuse University Z. Ahmed, J. Filippini, S. R. Golwala, D. Moore, R.W. Schnee, M. Kos, J. M. Kiveni R. W. Ogburn Texas A&M Case Western Reserve University R. Mahapatra D. S. Akerib, K. Clark, C. N. Bailey, D. R. Grant, R. Hennings-Yeomans, M.R. Dragowsky University of California, Berkeley M. Daal,, N. Mirabolfathi, B. Sadoulet, D. Seitz, B. Serfass, Fermilab D. Seitz, K. Sundqvist D. A. Bauer, F. DeJongh J. Hall, L. Hsu, D. Holmgren, E. Ramberg, J. Yoo University of California, Santa Barbara R. Bunker, D. O. Caldwell, H. Nelson, J. Sanders MIT E. Figueroa-Feliciano, S. Hertel, S. Leman, K. McCarthy University of Colorado at Denver M. E. Huber NIST K. Irwin University of Florida T. Saab, D. Balakishiyeva Queens University W. Rau University of Minnesota P. Cushman, L. Dong, M. Fritts, V. Mandic, X. Qiu, O. Kamaev, Santa Clara University A. Reisetter B. A. Young University of Zurich Stanford University S. Arrenberg, T. Bruch, L. Baudis, M. Tarka P.L. Brink, B. Cabrera, J. Cooley, M. Pyle, S. Yellin TAUP 09 Jodi Cooley - Stanford University 2

CDMS II: The Big Picture Use a combination of discrimination and shielding to maintain a “<1 event expected background” experiment with low temperature semiconductor detectors ER background Discrimination from measurements of E charge NR signal ionization and phonon energy . E phonon Keep backgrounds low as possible through shielding. TAUP 09 Jodi Cooley - Stanford University 3

CDMS II ZIP Detectors • Z-sensitive Ionization and Phonon mediated • 250 g Ge, 100 g Si crystals 1 cm thick, 7.5 cm diameter • Photolithographically patterned to collect phonon and ionization signals • xy position imaging • surface rejection from pulse shapes • 30 detectors stacked into 5 1 µ tungsten 380 µ x 60 µ aluminum fins towers of 6 detectors TAUP 09 Jodi Cooley - Stanford University 4

ZIP Detectors: Charge -3V -3V ~15% � Vetoed by guard ring Vetoed by guard ring h + h + h + ~85% e - e - e - • Inner Channel: Ionization Measurement • Outer Channel: Fiducial Volume TAUP 09 Jodi Cooley - Stanford University 5

ZIP Detectors: Phonons Al Collector quasiparticle W Transition- diffusion Edge Sensor ~ Si or Ge phonons ~ 10mK 4 4 SQUID readout channels, R TES ( Ω ) 3 each reads out 1036 TESs 2 Tungsten in parallel Transition Edge 1 Sensor (TES) T (mK) T c ~ 80mK TAUP 09 Jodi Cooley - Stanford University 6

Background Rejection • Most backgrounds (e, γ ) produce electron recoils Different Particles, Different Interactions Different particles, different interactions • WIMPS and neutrons produce nuclear recoils. M. Attisha TAUP 09 Jodi Cooley - Stanford University 7

Background Rejection • Most backgrounds (e, γ ) produce electron recoils • WIMPS and neutrons produce nuclear recoils. TAUP 09 Jodi Cooley - Stanford University 8

Background Rejection • Most backgrounds (e, γ ) produce electron recoils • WIMPS and neutrons produce nuclear recoils. • Ionization yield (ionization energy per unit phonon energy) strongly depends on particle type. TAUP 09 Jodi Cooley - Stanford University 8

Background Rejection • Most backgrounds (e, γ ) 1.5 produce electron recoils • WIMPS and neutrons 1 produce nuclear recoils. Ionization yield • Ionization yield (ionization energy per unit phonon 0.5 energy) strongly depends on particle type. 0 0 10 20 30 40 50 60 70 80 90 100 Recoil Energy (keV) TAUP 09 Jodi Cooley - Stanford University 8

Background Rejection • Most backgrounds (e, γ ) 1.5 produce electron recoils • WIMPS and neutrons 1 produce nuclear recoils. Ionization yield 0.5 • Particles that interact in the 0 0 10 20 30 40 50 60 70 80 90 100 Recoil Energy (keV) “surface dead layer” result in reduced ionization yield. TAUP 09 Jodi Cooley - Stanford University 9

Background Rejection • Most backgrounds (e, γ ) 1.5 produce electron recoils • WIMPS and neutrons 1 produce nuclear recoils. Ionization yield • Ionization yield (ionization energy per unit phonon 0.5 energy) strongly depends on particle type. • Particles that interact in the 0 0 10 20 30 40 50 60 70 80 90 100 Recoil Energy (keV) “surface dead layer” result in reduced ionization yield. TAUP 09 Jodi Cooley - Stanford University 9

Reduced Ionization Yield ~10 μ m “dead layer” -3V • Reduced charge yield carrier back diffusion h + h + h + e - due to charge carrier back-diffusion in h + h + h + e - e - surface events. rapid phonon down-conversion • “Dead-Layer” is e - e - e - within ~10 μ m of detector surface. TAUP 09 Jodi Cooley - Stanford University 10

Surface Event Rejection Bulk Surface Counts Delay + RiseTime [ µ s] Phonons near surface travel Selection criteria set to accept ~0.5 faster, resulting in shorter background events to preserve risetimes of phonon pulse. maximum nuclear recoil acceptance. TAUP 09 Jodi Cooley - Stanford University 11

Another View of Discrimination Bulk electron recoils Surface electron recoils Nuclear recoils 1 Ionization Yield 0.8 0.6 0.4 0.2 0 5 10 15 20 25 30 Timing Parameter ( µ s) TAUP 09 Jodi Cooley - Stanford University 12

Peeling the Shield Onion Active Muon Veto: rejects events from cosmic rays TAUP 09 Jodi Cooley - Stanford University 13

Peeling the Shield Onion Active Muon Veto: µ -metal (with copper inside) rejects events from cosmic rays Ancient lead Pb : shielding from gammas resulting from radioactivity 22.5 cm Polyethyene: moderate neutrons produced from fission decays and from ( α ,n) interactions 40 cm 10 cm resulting from U/Th decays Polyethylene Low Activity Lead TAUP 09 Jodi Cooley - Stanford University 14

Peeling the Shield Onion Active Muon Veto: rejects events from cosmic rays Pb : shielding from gammas resulting from radioactivity Polyethyene: moderate neutrons produced from fission decays and from ( α ,n) interactions resulting from U/Th decays Cu: shielding from gammas TAUP 09 Jodi Cooley - Stanford University 15

Peeling the Shield Onion Active Muon Veto: rejects events from cosmic rays Pb : shielding from gammas resulting from radioactivity Polyethyene: moderate neutrons produced from fission decays and from ( α ,n) interactions resulting from U/Th decays Cu: shielding from gammas NOTE: Cu lids for transport only. TAUP 09 Jodi Cooley - Stanford University 16

Peeling the Shield Onion Active Muon Veto: Phonon Sensors rejects events from cosmic rays Pb : shielding from gammas resulting from radioactivity Polyethyene: moderate neutrons produced from fission decays and from ( α ,n) interactions resulting from U/Th decays @ 40 mK!! Cu: shielding from gammas NOTE: Cu lids for transport only. TAUP 09 Jodi Cooley - Stanford University 16

TAUP 09 Jodi Cooley - Stanford University 17

SUF 17 mwe Log 10 (Muon Flux) (m -2 s -1 ) 0.5 n/d/kg (182.5 n/y/kg) Soudan 2090 mwe 0.05 n/y/kg SNOLAB 6060 mwe 0.2 n/y/ton (0.0002 n/y/kg) Depth (meters water equivalent) TAUP 09 Jodi Cooley - Stanford University 18

CDMS II Experiment • 30 detectors installed and operating in Soudan since June 06. • 4.75 kg of Ge, 1.1 kg of Si • Seven Total Data Runs: • R123 - R124: T4 T5 T3 • taken: (10/06 - 3/07) (4/07 - 7/07) • exposure: ~400 kg-d (Ge “raw”) • PRL 102, 011301 (2009) T1 T2 • R125 - R128 • taken: (7/07 - 1/08) (1/08 - 4/08) (5/08 - 8/08) (8/08 - 9/08) • exposure: ~ 750 kg-d (Ge “raw”) • Under Analysis • R129: • taken: (11/08 - 3/09) TAUP 09 Jodi Cooley - Stanford University 19

First Five Tower Results PRL 102, 011301 (2009) Blind Analysis: Event selection and efficiencies were calculated without looking at the signal region of the WIMP-search data. 1.5 Event Selection: Veto-anticoincidence cut 1 Ionization yield Single-scatter cut Q inner (fiducial volume) cut Ionization yield cut 0.5 Phonon timing cut Low yield singles masked 0 0 20 40 60 80 100 Recoil energy (keV) TAUP 09 Jodi Cooley - Stanford University 20

Analysis Summary PRL 102, 011301 (2009) 1 Quality, Singles, Veto Surface Background Fiducial volume Nuclear recoil acceptance 0.8 Nuclear recoil band Phonon timing Estimated number of background events to 0.6 pass surface cut in Ge 0.4 0 . 6 +0 . 5 − 0 . 3 ( stat. ) +0 . 3 − 0 . 2 ( syst. ) 0.2 0 5 10 15 20 25 30 35 40 45 50 Recoil energy (keV) Neutron Backround 398 raw kg-d Poly Cu ( α ,n): < 0.03 Pb (fission): < 0.1 121 kg-d WIMP equiv. @ 60 Cosmogenic: < 0.1 (MC 0.03-0.05) GeV/c 2 (10 - 100 keV 8 vetoed neutron multiples seen 0 vetoed singles seen analysis energy range) TAUP 09 Jodi Cooley - Stanford University 21

CDMS II Results NO EVENTS OBSERVED! Ionization yield 0.6 0.4 0.2 0 Ionization yield 0.6 0.4 0.2 0 0 20 40 60 80 100 Recoil energy (keV) PRL 102, 011301 (2009) TAUP 09 Jodi Cooley - Stanford University 22