First Results from the Cryogenic Dark Matter Search in the Soudan - PowerPoint PPT Presentation

First Results from the Cryogenic Dark Matter Search in the Soudan Underground Lab (astro-ph/0405033) Richard Schnee Case Western Reserve University

CDMS II Collaboration Stanford University Brown University P.L. Brink, B. Cabrera , J.P. Castle, M.J. Attisha, R.J. Gaitskell , J-P. F. Thompson C.L. Chang, M. Kurylowicz, L. Novak, R. W. Ogburn, T. Saab, A. Tomada Case Western Reserve University D.S. Akerib , M.R. Dragowsky, D.D.Driscoll, University of California, Berkeley S.Kamat, A.G. Manalaysay, T.A. Perera, J. Alvaro-Dean, M.S. Armel, J. Fillipini, R.W.Schnee, G.Wang A. Lu, V. Mandic, P.Meunier, N. Mirabolfathi, M.C.Perillo Isaac, W. University of Colorado at Denver Rau, B. Sadoulet , D.N.Seitz, B. Serfass, M. E. Huber G. Smith, A. Spadafora, K. Sundqvist Fermi National Accelerator Laboratory University of California, Santa Barbara D.A. Bauer , R. Choate, M.B. Crisler, R. Bunker, D.O. Caldwell, D. Callahan, R. Dixon, M. Haldeman, D. Holmgren, R.Ferril, D. Hale, S. Kyre, R. Mahapatra, B. Johnson, W.Johnson, M. Kozlovsky, J.May, H. Nelson , R. Nelson, J. Sander, D. Kubik, L. Kula, B. Lambin, B. Merkel, C.Savage, S.Yellin S. Morrison, S. Orr, E.Ramberg, R.L. Schmitt, Cryogenic J. Williams University of Florida Dark Lawrence Berkeley National Laboratory L. Baudis Matter J.H Emes, R. McDonald, R.R. Ross, A. Smith Search University of Minnesota Santa Clara University J. Beaty, P. Cushman , L. Duong, B.A. Young A. Reisetter Richard Schnee CDMS - Neutrino 2004

Really Cool Detectors: ZIPs Phonon D •250 g Ge or 100 g Si crystal SQUID array •1 cm thick x 7.5 cm diameter R bias R feedback •Photolithographic patterning I bias @50 mK •Collect athermal phonons z D A y x C B Q outer Q outer Z -sensitive Q inner Q inner I onization and V qbias P honon-mediated Measure ionization in low-field (~volts/cm) with segmented contacts to allow rejection of events near outer edge 1 µ tungsten 380 µ x 60 µ aluminum fins Richard Schnee CDMS - Neutrino 2004

Really Cool Detectors: ZIPs Phonon D •250 g Ge or 100 g Si crystal SQUID array •1 cm thick x 7.5 cm diameter R bias R feedback •Photolithographic patterning I bias @50 mK •Collect athermal phonons z D A y x C B Q outer Q outer Z -sensitive Photons from external source Q inner Q inner I onization and V qbias P honon-mediated Measure ionization in low-field (~volts/cm) with segmented Neutrons contacts to allow rejection of events near outer edge Richard Schnee CDMS - Neutrino 2004

Really Cool Detectors: ZIPs Phonon D •250 g Ge or 100 g Si crystal SQUID array •1 cm thick x 7.5 cm diameter R bias R feedback •Photolithographic patterning I bias @50 mK •Collect athermal phonons:  XY position imaging z D A y  Surface (Z) event veto based on pulse shape and timing x C B Q outer Q outer Z -sensitive Q inner Q inner I onization and V qbias P honon-mediated Y Measure ionization in low-field (~volts/cm) with segmented contacts to allow rejection of events near outer edge X Richard Schnee CDMS - Neutrino 2004

ZIP Z-Position Sensitivity Rejects Electrons • Events near crystal Surface- (Single-scatter) Neutrons surfaces produce photons electron from different frequency from recoils (selected 252 Cf spectrum of phonons 60 Co Source via nearest- source Phonon Risetime ( µ s) • These phonons neighbor multiple scatters from 60 Co travel faster, result in Accept source) a shorter risetime of the phonon pulse • Risetime cut eliminates the otherwise troublesome background Reject surface events >99% above 10 keV • Ionization Yield Richard Schnee CDMS - Neutrino 2004

More ZIP Z-Position Sensitivity • We are only Neutrons beginning to take full from advantage of the 252 Cf 31K information from the source Photons athermal phonon Accept from sensors! 133 Ba  Improving modeling of Source phonon physics  Extracting better discrimination parameters • Towards a full event reconstruction, near- Reject perfect rejection of Most neutrons pass timing cuts surface events Nearly no electron-recoils do! Richard Schnee CDMS - Neutrino 2004

CDMS II at Stanford and at Soudan •2001-2002 run at shallow site  28 kg day exposure of 4x 250g Ge detectors (and 2x 100g Si detectors)  20 nuclear-recoil candidates consistent with expected neutron background PRD 68:082002 (2003) 3 200 Hz muons 2 Stanford Underground Site Log 10 (Muon Flux) (m -2 s -1 ) in 4 m 2 shield 1 0 Oroville (USA) -1 Soudan (USA) -2 Kamioka (Japan) Boulby (UK) -3 Gran Sasso (Italy) -4 Frejus (France) Baksan (Russia) -5 Mont Blanc (France) Sudbury (Canada) -6 Kolar (India) -7 -8 0 2000 4000 6000 8000 10000 Depth (meters water equivalent) Richard Schnee CDMS - Neutrino 2004

CDMS II at Stanford and at Soudan •2001-2002 run at shallow site  28 kg day exposure of 4x 250g Ge detectors (and 2x 100g Si detectors)  20 nuclear-recoil candidates consistent with expected neutron background PRD 68:082002 (2003) 3 200 Hz muons 2 Stanford Underground Site Log 10 (Muon Flux) (m -2 s -1 ) in 4 m 2 shield 1 0 Oroville (USA) -1 Soudan (USA) -2 •2003-2005 in Soudan Mine, Minn. Kamioka (Japan) Boulby (UK) -3 1 per  Depth 713 m (2090 mwe) Gran Sasso (Italy) -4 Frejus (France) minute  Reduce neutron background Baksan (Russia) -5 Mont Blanc (France) in 4 m 2 shield from ~1 / kg / day Sudbury (Canada) to ~1 / kg / year -6 Kolar (India) -7 -8 0 2000 4000 6000 8000 10000 Depth (meters water equivalent) Richard Schnee CDMS - Neutrino 2004

Experimental Setup in the Soudan Mine DAQ/Electronics DAQ/Electronics RF-shielded RF-shielded Soudan II Soudan II Clean Clean room room HVAC HVAC Mezzanine Mezzanine Front-end Electronics MINOS MINOS Mechanical Mechanical Shield Detector Detector Prep Prep connecting connecting tunnel tunnel Pumps, Clean Benches Fridge Icebox Cryogenics Richard Schnee CDMS - Neutrino 2004

CDMS II Shielding •Active muon veto •40 cm outer polyethylene  Removes neutrons from ( α , n ) •22.5 cm lead shielding •10 cm inner polyethylene  Reduces neutrons from muons •Copper cryostat lead plastic scintillators outer polyethylene ancient inner lead polyethylene Richard Schnee CDMS - Neutrino 2004

First Run of CDMS II at Soudan • October 2003- January 2004 run of “Tower 1”  Same 4 Ge (1 kg) and 2 Si (0.2 kg) ZIPs run at Stanford  Photon and electron rejection both better than proposal  62 “raw” livedays, 53 livedays after cutting times of poor noise, etc. FET cards Nearly 85% livetime for SQUID cards last six weeks Calibration 4 K runs 0.6 K 0.06 K 0.02 K ZIP 1 (Ge) worse σ ZIP 2 (Ge) ZIP 3 (Ge) ZIP 4 (Si) ZIP 5 (Ge) 14 C 14 C 14 C ZIP 6 (Si) Richard Schnee CDMS - Neutrino 2004

In Situ Calibrations for Setting Cuts “Blind” After timing cuts, set to reject all Prior to timing cuts electron recoils in signal band 1.5 1.5 Z2/Z3/Z5 Z2/Z3/Z5 Ionization Yield Ionization Yield 1.0 13x our WIMP-search background 1.0 0.5 0.5 70% acceptance of neutrons 0.0 0.0 0 10 20 30 40 50 60 70 80 90 100 0 10 20 30 40 50 60 70 80 90 100 Recoil Energy (keV) Recoil Energy (keV) Blue points: electron recoils induced by a 133 Ba γ source Yellow points: nuclear recoils induced by a 252 Cf neutron source Richard Schnee CDMS - Neutrino 2004

Cuts and Efficiencies • Defined by calibration samples • Blind analysis: data on low-yield events from WIMP-search run `in the box’ until cut definitions completed • Opened box on March 20th Whoops… use of worse energy estimator discovered after box opened! we actually did blind analysis - - - - - - (non-blind) analysis we had intended Richard Schnee CDMS - Neutrino 2004

In Situ Photon Calibration with 133 Barium Phonons Ionization Expectations Expectations dN/dE Data Data dN/dE from simulation from simulation Recoil Energy (keV) Ionization Energy (keV) L. Baudis Richard Schnee CDMS - Neutrino 2004

In Situ Nuclear-recoil calibration with 252 Cf Nuclear recoils in Ge Ge ZIP ZIP Nuclear recoils in Si Si ZIP ZIP Nuclear recoils in Nuclear recoils in 10 4 Counts/ (keV kg day) Counts/ (keV kg day) Data Data 10 3 10 3 Expectations from simulation Expectations from simulation 10 2 10 2 Recoil Energy (keV) Recoil Energy (keV) Excellent agreement between data and Monte Carlo Excellent agreement between data and Monte Carlo Understand cut efficiencies ⇒ Understand cut efficiencies ⇒ S. Kamat Richard Schnee CDMS - Neutrino 2004

WIMP-search data with blind cuts After timing cuts, which Prior to timing cuts reject most electron recoils 10.4 keV Gallium line Z2/Z3/Z5 Z2/Z3/Z5 0.7 ± 0.35 misidentified electrons (w/Z1), 0.07 recoils from neutrons expected (w/ Z1) Richard Schnee CDMS - Neutrino 2004

WIMP-search data with non-blind cuts After timing cuts, which Prior to timing cuts reject most electron recoils 10.4 keV Gallium line 10.4 keV Gallium line Z2/Z3/Z5 1 nuclear-recoil candidate, Z2/Z3/Z5 consistent with backgrounds • Energy estimates improved 0.7 ± 0.35 misidentified electrons (w/Z1), • Some new events pass cuts 0.07 recoils from neutrons expected (w/ Z1) Richard Schnee CDMS - Neutrino 2004