Results from the Results from the Cryogenic Dark Matter Search Cryogenic Dark Matter Search at Soudan Soudan Underground Laboratory Underground Laboratory at (CDMS II) (CDMS II) Jonghee Yoo Jonghee Yoo Fermilab Fermilab The Dark Side of the Universe, Seoul Korea, 24 May 2005
CDMS II Collaboration 2 2 Brown University Stanford University M.J. Attisha, R.J. Gaitskell, J-P. F. Thompson P.L. Brink, B. Cabrera, C.L. Chang, J. Cooley, R.W. Ogburn, M. Pyle, S.Yellin Case Western Reserve Univers ity University of California, Berkeley D.S. Akerib, C. Bailey, P. Brusov, M.R. Dragowsky, D.D.Driscoll, D. Grant, R. Hennings- M. Daal, J. Filippini, A. Lu, V. Mandic, P.Meunier, Yeomans, S.Kamat, T.A. Perera, R.W.Schnee, N. Mirabolfathi, B. Sadoulet, D.N. Seitz, B. Serfass, G.Wang K.M. Sundqvist Fermi National Accelerator Laboratory University of California, Santa Barbara D.A. Bauer, M.B. Crisler, R. Dixon, D. Holmgren, R. Bunker, D.O. Caldwell, R. Ferril, R. Mahapatra, E.Ramberg, J. J. Yoo Yoo H. Nelson, J. Sander, Lawrence Berkeley National Laboratory University of Colorado at Denver and Health Sciences Center R. McDonald, R.R. Ross, A. Smith M. E. Huber National Institute for Standards and Technology University of Florida K. Irwin L. Baudis, S. Leclercq Santa Clara University University of Minnesota B.A. Young P. Cushman, L. Duong, A. Reisetter The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
Evidences of the Missing Components 3 3 Rotation curves curves of of galaxies galaxies CMB Rotation CMB Large Scale Scale Structure Structure Large SuperNova Ia SuperNova Ia Galaxy clusters Gravitational Lensing Galaxy clusters Gravitational Lensing The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
Budget of the Universe 4 4 Baryonic Dark Matter Dust, Gas MACHOs Upper limit by BBN light element ratio observations Hot Dark Matter Upper limit from CMB, tritium decay neutrino mass Ω ν < 0.0155 Cold Dark Matter In the picture of Λ CDM model WIMPs / Axions / … WMAP and SDSS observations The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
World Map of Dark Matter & Where We Are 5 5 CDMS Limit Plotter for Public : http://dmtools.brown.edu 90%CL L. Roszkowski The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
WIMP Distribution in the Universe 6 6 Photo from Z.Frei and E.Gunn 2 ) • Spherical Halo Model Spherical Halo Model • ( � ~ 1/ r • Energy spectrum & rate depend on WIMP distribution in Dark Matter Halo Energy spectrum & rate depend on WIMP distribution in Dark Matter Halo • v esc dR f ( v ) � dv dE � �� v v min – Assume isothermal Maxwell-Boltzmann velocity distribution Assume isothermal Maxwell-Boltzmann velocity distribution – – Vo= 230 Vo= 230 km/s km/s (WIMP velocity against detector) (WIMP velocity against detector) – – Vesc= Vesc= 650 650 km/s km/s (escape velocity of WIMP (escape velocity of WIMP from galactic halo) from galactic halo) – – ρ = 0.3 GeV / cm 3 3 – ρ = 0.3 GeV / cm – Energy spectrum of recoils is featureless exponential with Energy spectrum of recoils is featureless exponential with <E> ~ 50 <E> ~ 50 keV keV – The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
Invisible … 7 7 Yoo steal this figure from http://dmrc.snu.ac.kr What is essential is invisible to the eye. Now here is secret of CDMS, a very simple secret: If you can not see… Listen! The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
WIMP Detection Strategy of CDMS 8 8 WIMP Direct detection of WIMP signal Nuclei recoil by elastic scattering Read out phonons from recoil together with ionization signal Weakly Interacting WIMP mean free path in Ge ~ 10 10 m The event will single scatter Interaction Rate ∝ A 2 Use both Ge(73) and Si(28) targets R(Si/Ge) = ~1/6 The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
CDMS Detector 9 9 380 µ x 60 µ aluminum fins 1 µ tungsten ~10mK quasiparticle Transition R diffusion Edge Sensor Al T ElectroThermal Ge or Si Feedback Tc~80mK phonons The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
CDMS Detector Readout 10 10 Phonon signal A D From a quadrant Phonon sensor B C Recoil energy Charge signal From inner electrode Charge sensor Ionization energy The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
WIMP event and Background 11 11 WIMP event Background Nucleus E r Recoils E r v/c ≈ 0.3 v/c ≈ 7 × 10 -4 Electron γ Recoils Less ionization More ionization χ 0 The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
WIMP Signal and Background 12 12 Yield = E(ionization) / E(recoil) Photons Photons Neutrons Neutrons The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
WIMP Candidate Signal (a fake example) 13 13 TOWER 1 TOWER 2 VETOs Time[us] 0 200 400 600 800 1000 1200 Time[us] 0 200 400 600 800 1000 1200 The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
Neutron Background 14 14 To prevent neutron background 1. Go deep underground to reduce the cosmogenic production of neutrons 2. Veto out cosmic muons : active shield 3. Shield the detectors with lead and polyethylene : passive shield Statistical Discrimination of neutron background 1. Measure the rate of multiple interaction 2. Compare the rates in Si vs Ge : WIMP cross sections scale as A 2 , while neutron rates will be comparable The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
CDMS at Stanford (Single Tower) 15 15 • 2001-2002 operation at shallow site (17 mwe) – 28 kg-days net exposure of 4 x 250g Ge detectors and 2 x 100g Si detectors – 20 nuclear-recoil candidates consistent with expected neutron background – PRD 68, 082002 (2003) : Single Tower Results from Stanford Log 10 (Muon Flux) (m -2 s -1 ) 200 muons muons /sec /sec 200 Stanford Stanford in 4 m in 4 m 2 2 shield shield Underground Site Underground Site Oroville (USA) Soudan (USA) Boulby (UK) Gran Sasso (Italy) Frejus (France) Baksan (Russia) Mont Blanc (France) Sudbury (Canada) Kolar (India) Depth (meters water equivalent) The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
CDMS II at Soudan (Single Tower) 16 16 • 2003 operation at deeper site – 2090 m.w.e @ Soudan Mine (5 x 10^4 fewer muons) – Reduced neutron background from ~1/kg/day to ~1/kg/year Log 10 (Muon Flux) (m -2 s -1 ) 200 muons/sec muons/sec 200 Stanford Stanford in 4 m in 4 m 2 2 shield shield Underground Underground Site Site Oroville (USA) 1 muons muons / min / min 1 Soudan (USA) in 4 m 2 2 shield in 4 m shield Boulby (UK) Gran Sasso (Italy) Frejus (France) Baksan (Russia) Mont Blanc (France) Sudbury (Canada) Kolar (India) Depth (meters water equivalent) The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
Experimental Setup in the Soudan Mine 17 17 Surface CDMS MINOS 780m (2090mwe) The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
Detector Shielding 18 18 µ -metal (with copper inside) Ancient lead 23 14 41 cm Polyethylene Low Activity Lead The Dark Side of the Universe, Seoul Korea J.Yoo (Fermilab)
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