The Cryogenic Dark Matter Search “From our home on the Earth, we look out into the distances and strive to imagine the sort of world into which we are born…” - Edwin Hubble Jeter Hall Fermilab Center for Particle Astrophysics

Identification of Dark Matter 2008 August 19 A Dark Matter Revolution Exciting time for dark matter Exciting time for dark matter Backgrounds Backgrounds WIMP annihilation in the cosmos

Identification of Dark Matter 2008 August 19 The WIMP candidates WIMPs are still viable, and perhaps favored WIMPs are still viable, and perhaps favored Direct detection may be insurmountably challenging Direct detection may be insurmountably challenging

Identification of Dark Matter 2008 August 19 Direct Detection of Dark Matter Search for neutral scattering in terrestrial detectors Search for neutral scattering in terrestrial detectors For 100 GeV neutralinos, interaction energy ~10s keV rate <0.01 events / day / kg For 100 GeV neutralinos, interaction energy ~10s keV rate <0.01 events / day / kg WIMP detector energy transferred appears in ‘wake’ of recoiling nucleus WIMP-Nucleus Scattering

Identification of Dark Matter 2008 August 19 Shielding/Radiopurity 2000 m.w.e. rock overburden 2000 m.w.e. rock overburden Plastic scintillator active veto Plastic scintillator active veto 20 cm lead 20 cm lead 50 cm polyethylene 50 cm polyethylene Copper cryostat Copper cryostat 1 mm silicon endcaps 1 mm silicon endcaps Gaps between detectors minimized Gaps between detectors minimized Rigorous cleanliness Rigorous cleanliness

Identification of Dark Matter 2008 August 19 ZIP Detectors 30 detectors 30 detectors 11 Si kg 11 Si kg 19 Ge kg 19 Ge kg 2 ionization collection electrodes 2 ionization collection electrodes 4 phonon sensor arrays 4 phonon sensor arrays Phonon sensor Recoil energy A CB D Charge sensor Ionization energy

Identification of Dark Matter 2008 August 19 Phonon Sensors Tungsten transition edge sensors (Tc ~ 80 mK) Tungsten transition edge sensors (Tc ~ 80 mK) Superconducting aluminum collector fins Superconducting aluminum collector fins A CB D 1  tungsten 380  x 60  aluminum fins Electro Thermal Feedback R T Tc~80mK ~10mK

Identification of Dark Matter 2008 August 19 Residual Gamma Backgrounds Residual gamma background due to U, Th, K contamination and neutron activation at ~ few / keV / kg / day Residual gamma background due to U, Th, K contamination and neutron activation at ~ few / keV / kg / day Nuclear recoils leave a majority of energy in atomic motion Nuclear recoils leave a majority of energy in atomic motion After cuts expect gamma acceptance of ~ / kg / day After cuts expect gamma acceptance of ~ / kg / day Yield = E(ionization) / E(recoil) Yield Rejection ~ 10 5 : 1 Singles (<~0.5 keV in other detectors) Singles Acceptance ~ 5:1

Identification of Dark Matter 2008 August 19 Residual Surface Backgrounds Surface backgrounds due to low energy beta and possibly gamma radiation Surface backgrounds due to low energy beta and possibly gamma radiation Back diffusion of electrons/holes reduces measured ionization energy Back diffusion of electrons/holes reduces measured ionization energy Single scatter surface event rate ~0.4 / kg / day Single scatter surface event rate ~0.4 / kg / day See S. Golwala’s presentation “Identification of the Surface-Event Background in the CDMS II Experiment” Thursday 13:55 See S. Golwala’s presentation “Identification of the Surface-Event Background in the CDMS II Experiment” Thursday 13:55 Experiment Monte Carlo 85 keV  63 keV  22 keV  88 keV  22 keV  ~10μm “dead layer”

Identification of Dark Matter 2008 August 19 Residual Surface Backgrounds Surface events are faster due to rapid phonon down-conversion Surface events are faster due to rapid phonon down-conversion Cut on timing (delay + risetime) Cut on timing (delay + risetime) Surface event acceptance ~1:200, after cuts background rate ~.002 events / kg / day Surface event acceptance ~1:200, after cuts background rate ~.002 events / kg / day Dominant background, but rejection can be improved with mild loss of efficiency Dominant background, but rejection can be improved with mild loss of efficiency acceptance region γ ( 133 Ba) β ( 133 Ba) n ( 252 Cf)

Identification of Dark Matter 2008 August 19 Neutron Backgrounds Neutron acceptance ~30% Neutron acceptance ~30% Expect ~0.01 neutrons / kg / day from cosmic radiation Expect ~0.01 neutrons / kg / day from cosmic radiation Veto rejection ~1000:1 leaving ~2x10 -5 / kg / day Veto rejection ~1000:1 leaving ~2x10 -5 / kg / day Expect <3x10 -4 neutrons / kg / day from (alpha,n) and fission Expect <3x10 -4 neutrons / kg / day from (alpha,n) and fission Estimate dominated by uncertain lead contamination Estimate dominated by uncertain lead contamination

Identification of Dark Matter 2008 August 19 Soudan Exposure R118 (2003-4) R118 (2003-4) 1 tower, 1 kg Ge, 0.2 kg Si 1 tower, 1 kg Ge, 0.2 kg Si 52.4 live days 52.4 live days PRL 93, (2004) PRL 93, (2004) PRD 72, (2005) PRD 72, (2005) R119 (2004) R119 (2004) 2 towers, 1.5 kg Ge, 0.4 kg Si 2 towers, 1.5 kg Ge, 0.4 kg Si 74.5 live days 74.5 live days PRL 96, (2006) PRL 96, (2006) R123/4 (2006-7) R123/4 (2006-7) 5 towers, 4.75 kg Ge, 1.1 kg Si 5 towers, 4.75 kg Ge, 1.1 kg Si 163 live days 163 live days R125-Present R125-Present 5 towers 5 towers 240 live days (analysis ongoing) 240 live days (analysis ongoing)

Identification of Dark Matter 2008 August 19 R123/4 Signal Region After cuts ~120 kg days WIMP effective exposure After cuts ~120 kg days WIMP effective exposure ± 0.5 (stat) background events expected No events in signal region (arXiv: ) No events in signal region (arXiv: ) R123/4 events Neutron events Signal Region ****

Identification of Dark Matter 2008 August 19 CDMS-II WIMP Limits World class sensitivity to WIMP-nucleon scattering World class sensitivity to WIMP-nucleon scattering Analysis ongoing with >2x data Analysis ongoing with >2x data arXiv: arXiv:

Identification of Dark Matter 2008 August 19 Future of CDMS Additional analysis Additional analysis more data ~3x sensitivity more data ~3x sensitivity Solar axion search (see T. Bruch poster) Solar axion search (see T. Bruch poster) Lower threshold analysis Lower threshold analysis Additional running Additional running Possible low threshold runs Possible low threshold runs Super Tower 1 in early 2009 (2.75 kg more Ge) Super Tower 1 in early 2009 (2.75 kg more Ge) Super Towers 2-4 in 2010 (additional 9 kg Ge) Super Towers 2-4 in 2010 (additional 9 kg Ge) And beyond And beyond Massive 6” diameter ZIP detectors Massive 6” diameter ZIP detectors Kinetic inductance phonon sensors Kinetic inductance phonon sensors Multiplexing Multiplexing Phonon sensors on both faces Phonon sensors on both faces Move to SNOLAB, reduce apparatus backgrounds, improve stability Move to SNOLAB, reduce apparatus backgrounds, improve stability …

Identification of Dark Matter 2008 August 19 The CDMS Collaboration Brown University M. Attisha, R. Gaitskell Caltech Z. Ahmed, S. Golwala, D. Moore, R.W. Ogburn Case Western Reserve University D. Akerib, C. Bailey, K. Clark, M. Danowski, M. Dragowsky, D. Grant, R. Hennings-Yeomans Fermilab D. Bauer, F. DeJongh, J. Hall, D. Holmgren, L. Hsu, E. Ramberg, R. Schmitt, J. Yoo MIT E. Figueroa-Feliciano, S. Hertel, S. Leman, K. McCarthy, P. Wikus Queens University W. Rau Santa Clara University B. Young Stanford University P.L. Brink, B. Cabrera, J. Cooley, L. Novak, M. Pyle, A. Tomada, S. Yellin Syracuse University M.Kiveni, M. Kos, R. Schnee University of California, Berkeley M. Daal, J. Filippini, N. Mirabolfathi, B. Sadoulet, D. Seitz, B. Serfass, K. Sundqvist University of California, Santa Barbara R. Bunker, D. Caldwell, R. Mahapatra, H. Nelson, J. Sander University of Colorado, Denver B. Hines, M. Huber University of Florida A. Achelashvili, D. Balakishiyeva, T. Saab, G. Sardane University of Minnesota J. Beaty, P. Cushman, L. Duong, M. Fritts, O. Kamaev, V. Mandic, X. Qiu, A. Reisetter University of Zurich S. Arrenberg, T. Bruch, L. Baudis, M. Tarka Also see: Poster by T. Bruch (search for solar axions) Oral presentation by S. Golwala (identification of the surface background) “For I can end as I began. From our home on the Earth, we look out into the distances and strive to imagine the sort of world into which we are born… The search will continue. The urge is older than history. It is not satisfied and it will not be suppressed.” - Edwin Hubble

Identification of Dark Matter 2008 August 19 The Dark Matter Problem Dark matter hypothesis explains many observations Dark matter hypothesis explains many observations Modifying gravity still viable, but not favored Modifying gravity still viable, but not favored