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Cryogenic Dark Matter Search Harry Nelson UCSB Journal Club March 12, 2004 HNN CDMS Collaboration Brown University Stanford University M. Attisha, R.J. Gaitskell, J-P. Thompson Case Western Reserve University D.S. Akerib, M.R. Dragowsky, D.Driscoll, S. Kamat, T.A. Perera, R.W. Schnee, G.Wang Fermi National Accelerator Laboratory D.A. Bauer, M.B. Crisler, R. Dixon, D. Holmgren, E. Ramberg Lawrence Berkeley National Laboratory J.H Emes, R.R. Ross, A. Smith Princeton University T. Shutt Santa Clara University B.A. Young 3/12/04 UCSB Cryogenic Dark Matter Search L. Baudis, P.L. Brink, B. Cabrera, C. Chang, W. Ogburn, T. Saab University of California, Berkeley M.S. Armel, A. Lu, V. Mandic, P.Meunier, N. Mirabolfathi, W. Rau, B. Sadoulet, D. Seitz, A. Spadafora, K. Sundqvist University of California, Santa Barbara R. Bunker, D.O. Caldwell, R. Ferril, R. Mahapatra, H. Nelson, J. Sander, C. Savage, S. Yellin University of Colorado at Denver M. E. Huber University of Minnesota P. Cushman, L. Duong, A. Reisetter Cornell Journal Club 2 HNN UCSB Plan z Massive Dark Matter z Direct Detection z The ZIP Detector z Data z Future 3/12/04 Cornell Journal Club 3 HNN Primack Pyramid UCSB We are 1 in 10,000 of the energy in Universe… Our form of matter less than dark matter by factor of 5 or so in energy... Who ordered that? 3/12/04 Cornell Journal Club 4 HNN Leading Thinkers 3/12/04 Cornell Journal Club UCSB 5 HNN z Origin of Dark Matter During inflation ⟩ ⟩ Axion, superpartner Axino *Zillas →Could ⟩ z UCSB have only gravitational interactions! Few constraints… During thermal equilibration phase of Big Bang… ⟩ ⟩ 3/12/04 m > few keV (currently observed large scale structure) m > 10 or so GeV (nothing new at accelerators) Cornell Journal Club 6 HNN UCSB Candidates 3/12/04 Cornell Journal Club 7 HNN UCSB Coincidence or Clue… `WIMP’ ’ 3/12/04 Cornell Journal Club 8 HNN WIMP/nucleon σ≈10-42 cm UCSB Exper. CDMS DAMA Theory SUSY: various constraints including Big Bang 3/12/04 Cornell Journal Club 9 HNN Galactic Dark Matter UCSB R is the distance from center v v is the speed (tangential) R 3/12/04 Cornell Journal Club 10 HNN UCSB The Dark Ball Bulge 3/12/04 Disk Cornell Journal Club Dark Matter `Halo’ (aka Aura) 11 HNN UCSB What about our home galaxy (Milky Way)? χ χ χ χ χ χ χ χ χ χχ χ χ χ χχ χ χ χ χ χ χ χ χ χ χ Honma and Sofue, 1996 v 220 km/s Without the Dark Halo (Binney & Tremaine) ∆:v0=180 km/s ⊕ 3/12/04 Cornell Journal Club R 12 HNN From Galactic Astrophysics… z Local energy density, speed of DM MeV ú 0 ø 300 3 cm 0? (200-2000) z UCSB DM at rest: 3/12/04 km v 0 ø 220 (ì 0 ø 7 â 10 à4) s (ì 20 ø 12 â 10 à6) (170-270) ⟨vDM⟩=0 (sun plowing through at v0 ≈ 220 km/s) 2 ⟩1/2 ≈ 300 km/s… useful to approximate ≈ 0 ⟨vDM Cornell Journal Club 13 HNN Direct Detection: Signal and Main Background Signal Nucleus Recoils Background Electron Recoils Er v/c ≈ 7×10-4 dense energy deposition ionization efficiency low distinct ionization energy scale 0 χ (calibrate: neutron) 3/12/04 UCSB γ Er v/c ≈ 0.3 Sparse Energy Deposition Differences the Basis of Particle ID Cornell Journal Club 14 HNN Rate of Main Background UCSB ≡ DRU • Shield (shield radioactive too!)… 1 ev/(kg d keV) typical • Reduce the background… HDMS , IGEX , Genius • Exploit astron. properties (year cycle, directionality) DAMA, DRIFT • Devise detectors that can distinguish nuclear recoil from electron recoil… Edelweiss, CDMS, Xenon.. 3/12/04 Cornell Journal Club 15 HNN UCSB Nuclear Recoil – Cross Section ∝A4 `scalar’ or SI (Spin Independent) 3/12/04 Cornell Journal Club 16 HNN Nuclear Recoil – Diffraction UCSB Iodine (A=127) DAMA 0 110 220 330 keV ER 3/12/04 Cornell Journal Club 17 HNN UCSB Nuclear Recoils from Massive Dark Matter z Deposit 10’s of keV; high target A favored z Target A<<160, dark matter velocity spectrum a delta-function, recoil spectrum flat up to endpoint. z Dark matter spectrum roughly maxwellian… recoil spectrum ends up exponentially falling z Form factor of nucleus directly appears in recoil spectrum 3/12/04 Cornell Journal Club 18 UCSB Copper NaI Lead PMT DAMA – 100 kg of NaI, no particle ID PMT HNN Poly Sodium, A=23 Eobs(KeVee)≈0.25 Erecoil (KeV) Erecoil → Light Iodine, A=127 Eobs(KeVee)≈0.09 Erecoil (KeV) 3/12/04 Cornell Journal Club 19 HNN Annual Modulation in Rate UCSB • `Usual Simplification’: Halo particles are at rest, on average 2 1/2 ⟨vDM⟩ =0 km/s • Sun moves through Halo - `apparent’ wind • Earth modulates `wind’ velocity yearly v k = 15 km/s 2 ⟨vDM⟩1/2 ≈ 300 km/s Fig. from DRIFT DAMA at Gran Sasso Peak-to-peak up to 40% 3/12/04 Cornell Journal Club 20 HNN DAMA Background and Signal UCSB 0.0195±0.031 -0.0001±0.019 cpd/kg/keV Energy Spectrum Bkgd ≈ 1 cpd/kg/keV 2-6 KeV 8-24 KeV Na(23) 20-70 KeV I(127) through through2000 2003… …4σ 6.3 σ Bernabei et al., astro-ph/0307403 3/12/04 Cornell Journal Club 21 HNN UCSB DAMA noise... >1 pe threshold <10-4 cpd... 3/12/04 Cornell Journal Club 22 HNN Particle ID/Discrimination (by DRIFT) 40 keV Ar in 1/20 atm Ar UCSB 13 keV e- in 1/20 atm Ar Ar pushes other Ar atoms, none go very far. Electron pushes other electrons, all go far 5 cm 3/12/04 Cornell Journal Club 23 HNN UCSB Discrimination Techniques 1) Time Structure of the Pulse 2) Pulse Height/Area via: • Ionization (like Ge) • Scintillation (like NaI) • Heat/Phonons • Physical Size of Ionization Liquid Xenon Also a scintillator 1 0.1 (Spooner) 0.01 e- recoils from γ’s 0.001 0.0001 NaI 0.00001 1 NaI 10 100 pulse time constant (ns) 1 Nuclear recoils From neutrons γ’s 0.1 DAMA does not use this 10-20keV (50-100 keV ER) 0.01 0.001 ER: 130-150 KeV (I) ⟨t⟩ 0.0001 0.00001 1 1 Gerbier et al., 1998 3/12/04 Width of pulse Cornell Journal Club 10 10 pulse time constant ns ⟨t⟩ (ns) 100 100 24 HNN Catalog of Recoil Experiments UCSB Rick Gaitskell 3/12/04 Cornell Journal Club 25 HNN CDMS Technique: Phonons v. Ionization Nuclear recoils (induced by a neutron source) UCSB Electron recoils (induced by a γ source) Slope really 1! Ionization =1 (bkgd) ≈1/3 (sig) Phonons Egap = 3/4 eV w = 3 eV (Ge) Shutt et al., 1992 3/12/04 Cornell Journal Club 26 HNN Our Detectors (Ge/Si 30 mK) UCSB Phonon D SQUID array Rbias One side: `Phono cathode’ Transition Edge Sensors Segmented for x,y imaging Rfeedback I bias D A C B Q outer Q inner Vqbias 7.5 cm 3/12/04 Other side: charge collection 2 segments to reject edge events Cornell Journal Club 27 HNN The ZIP Phono`cathode’... 1 µ tungsten UCSB 380µ x 60µ aluminum fins • 4 segments + timing to get x,y on the face • rise time to get z, into the face 3/12/04 Cornell Journal Club 28 HNN UCSB Technology of `ZIP’s (Z for z) The `phono-cathode’… quasiparticle trap W quasiparticle Transition-Edge diffusion Sensor (TES) Al Collector Cooper Pair Al Si or Ge phonons ~ 10mK RTES (Ω) • Signal much faster microseconds • 3-d imaging (Z) 4 3 2 1 superconducting 3/12/04 normal Cornell Journal Club Tc ~ 80mK T (mK) 29 HNN UCSB Pulses Charge (Q) • Charge signals are virtually instantaneous 20 keV Phonons (P) µ = 10.4 keV σ = 0.34 keV • Phonon start times are measured relative to charge signal • Can `triangulate’ timing to reconstruct x, y… • Risetime gives z (along thin direction of detector) 3/12/04 Cornell Journal Club 30 HNN Calibration Data UCSB 1334 Photons (external source) 233 External Electrons (β) (tagged contamination) 616 Neutrons (external source) 3/12/04 Cornell Journal Club 31 HNN Incomplete Ionization Collection... External β z Electrode Germanium Implants UCSB Ionization electrons get trapped in this electrode 1 E Those electrons never drift over to the other electrode… ionization signal reduced… but, all the phonons/heat still present… (ionization)/(phonons) < 1 Measure z with pulse risetime 3/12/04 Cornell Journal Club 32 HNN ZIP Surface Electron Rejection UCSB (Single-scatter) Neutrons Surfaceelectron recoils photons from from (selected via nearest- 60Co Source 252Cf neighbor multiple source scatters from 60Co source) Accept Surface electrons still likely to be the limiting background 3/12/04 Reject Cornell Journal Club 33 HNN UCSB Signal Shape ∝A2 Nucleus Recoils MWIMP=100 GeV σ = 10-42 cm2/nucleon Silicon, Sulphur Germanium Iodine, Xenon Er Slope: Maxwell-Boltzmann Diffraction off Nucleus WIMPs in Galaxy χ0 3/12/04 Cornell Journal Club 34 HNN UCSB CDMS Sites Stanford (through 2002): • 17 mwe - shallow • Substantial neutron flux • Results (28 of 50 kg-d) scintillator veto polyethylene outer moderator 3/12/04 outer Pb shield detectors Icebox inner Pb shield Soudan Site (online 10/2003): • 2100 mwe • Neutron flux down 1/300 • 30 kg-d bkgd-free dilution • Mass just roughly doubled refrigerator Cornell Journal Club 35 HNN Shallow Site Data UCSB Just one detector hit FET cards SQUID cards 4K 0.6 K 0.06 K 0.02 K ZIP 1 (Ge) ZIP 2 (Ge) ZIP 3 (Ge) ZIP 4 (Si) ZIP 5 (Ge) ZIP 6 (Si) Surface electrons Z1 (×) or Z5 (+) 8 cm NR Band (22) 4 Germanium Detectors (0.66 kg total) 2 Silicon Detectors (0.2 kg total) → Small DM rate, high neutron rate 3/12/04 Cornell Journal Club 36 HNN CDMS: not deep… neutron background UCSB 17 mwe µ µ Active Muon Veto Pb Shield n Copper n Fridge Polyethylene Detectors Inner Pb shield ... Experiment moved to Soudan, 2100 mwe depth 3/12/04 Cornell Journal Club 37 More Proof: Multiple Scattering photons Nonneighbor doublescatter U Triplescatter z z z • 3 here + MC: 16±9 single scatter see 22-2=20 3/12/04 neutrons Cornell Journal Club UCSB Size & color indicates yield in third detector HNN 38 HNN Candidate Energy Spectrum UCSB Expected shape if detection efficiencies were 100%, neutrons Expected spectrum including detection efficiencies, normalized to expected # of events (resembles 20 GeV WIMP!!) 3/12/04 Cornell Journal Club 39 HNN UCSB Limits 90% CL upper limits assuming standard halo, A2 scaling ZEPLIN -I New CDMS limits, 28 kg-d no bkgd sub, w/bkgd sub, expected er p p U iss e w × Lim it el d E MSSM models 300X lower neutron background expected at Soudan… have 30 kg-d 3/12/04 Cornell Journal Club 40 HNN UCSB Soudan 2341 ft of hard rock shielding 3/12/04 Cornell Journal Club 41 HNN UCSB More Soudan 3/12/04 Cornell Journal Club 42 HNN Soudan Calibration Data Looks Good Californium Source (n and gamma) UCSB Barium Source (gamma) … 30 kg-d `low background’ collected, processed, blinded…. results April?? 3/12/04 Cornell Journal Club 43 HNN UCSB Where should we get? For more limit curves, see http://dmtools.berkeley.edu, Gaitskell & Mandic Current CDMS Limit eis w l e Ed mit i L sion u l c s Ex SUSY gµ-2 (Baltz&Gondolo, PRL 86 (2001) 5004) No SUSY gµ-2 constraint 3/12/04 Cornell Journal Club Expected sensitivity of completed CDMS run at Soudan (5x better than current limit). Projected sensitivity for CDMS at Soudan, with 5 towers 4 kg Ge, 1.5 kg Si: 0.1 events/kg/keV/year (100x better than current limit). 44 Lots of competition... UCSB Rick Gaitskell HNN 3/12/04 Cornell Journal Club 45 HNN Prognostication 3/12/04 Cornell Journal Club UCSB 46
