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Searches for Dark Matter (the Quest)

Searches for Dark Matter (the Quest). Harry Nelson UCSB 2003 SLAC Summer Insitute Aug. 5-6 2003. Recap - Direct Detection. How to dredge the small (0.01 DRU= ev/(kg d keV)) up out of a bigger background (1 DRU typical) of recoil electrons from comptons?.

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Searches for Dark Matter (the Quest)

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  1. Searches for Dark Matter(the Quest) Harry Nelson UCSB 2003 SLAC Summer Insitute Aug. 5-6 2003

  2. Recap - Direct Detection How to dredge the small (0.01 DRU= ev/(kg d keV)) up out of a bigger background (1 DRU typical) of recoil electrons from comptons? • Shield (shield radioactive too!)… 1 ev/(kg d keV) typical  • Reduce the background… HDMS , IGEX , Genius  • Exploit astron. propert. (year cycle, directionality) DAMA, DRIFT  • Devise detectors that can distinguish nuclear recoil from electron recoil… Edelweiss, CDMS, Xenon.. Indirect Detection (milli-) Charged Massive Particles Closing SLAC Summer Institute

  3. 2 vDM1/2 =0 km/s vDM1/2  300 km/s 2 DAMA at Gran Sasso Peak-to-peak up to 40% Annual Modulation in Rate • `Usual Simplification’: Halo particles are at rest, on average • Sun moves through Halo - `apparent’ wind • Earth modulates `wind’ velocity yearly Fig. from DRIFT SLAC Summer Institute

  4. Daily Modulation in Direction • Recoiling Nucleus Follows the Initial WIMP Direction… the `wind’ • Detector gaseous to reconstruct recoil direction • DRIFT at Boulby (Spooner) Fig. from DRIFT SLAC Summer Institute

  5. NaI PMT PMT Copper Lead Poly Sodium, A=23 Eobs(KeVee)0.25 Erecoil (KeV) Erecoil  Light Iodine, A=127 Eobs(KeVee)0.09 Erecoil (KeV) DAMA – 100 kg of NaI SLAC Summer Institute

  6. 0.01950.031 -0.00010.019 cpd/kg/keV Energy Spectrum Bkgd  1 cpd/kg/keV 8-24 KeV Na(23) 20-70 KeV I(127) 2-6 KeV through 2000 … 4 through 2003 … 6.3  Bernabei et al., astro-ph/0307403 DAMA Background and Signal SLAC Summer Institute

  7. DAMA noise... >1 pe threshold <10-4 cpd... SLAC Summer Institute

  8. DAMA Allowed Regions p (cm2), =0 / through 2000 (standard halo) through 2003 Na 10-44 3 10-42 4 I • Variation mainly due to changes in halo parameters • two plots not directly comparable (different halos used) • With new result, DAMA ceases to employ `standard Maxwellian halo’ - comparisons challenging SLAC Summer Institute

  9. Halo Variation Kamionkowski and Kinkhabwala (1997) SLAC Summer Institute

  10. A2  2 J(J+1) J0  unpaired nucleon, odd A p (cm2) Couple to neutron spin 10-34 10-36 NAIAD (Boulby) (couple to proton spin) DAMA Perhaps WIMP couples not to nucleons, but to their spin S,V,T,A,P  S,A non-relativistic (V too) S - `nucleon, SI’ (or V) … A - `spin or SD’ (also, could break isospin… np) LIBRA 250kg, NAIAD continues, ANAIS in Spain... SLAC Summer Institute

  11. Background Electron Recoils Er v/c  0.3 Sparse Energy Deposition  Discrimination of Recoils Signal Nucleus Recoils Er v/c  710-4 Dense Energy Deposition v/c small; Bragg 0 Differences the Basis of Discrimination SLAC Summer Institute

  12. Ar pushes other Ar atoms, none go very far. Electron pushes other electrons, all go far Simulation (by DRIFT) 40 keV Ar in 1/20 atm Ar 13 keV e- in 1/20 atm Ar 5 cm SLAC Summer Institute

  13. dE/dx for different recoils http://www.srim.org/SRIM/SRIM2003.htm Strategies Detector insensitive to small dE/dx (track etch, SDD) Convert E to two distinct measured quantities that look different depending on whether nuclear recoil or electron. SLAC Summer Institute

  14. Track Etch Detectors Struck Nucleus Corrosive Etch Mica, CR39 Large dE/dx Ancient Mica 0.5109 yr Exposure fraction mm2 area 100 Å http://moedal.web.cern.ch/moedal/moedal_track.htm SLAC Summer Institute

  15. Mica Result Snoden-Ifft, Freeman, Price (1994) 58% 16O 16% 28Si 12% 27Al 5% 39K p (cm2)10-37cm2 SD: 10-33cm2 SLAC Summer Institute

  16. 15 gm 0 Spin Dependent Superheated Droplet Detector (SDD) Target, C2ClF5 (Liquid): Temp. > Boiling Gelatin 10-36 cm2 10 m Collar et al., (2000) SLAC Summer Institute

  17. Lose the Gelatin… get all Target Really a bubble chamber... CF3Br Juan Collar and Andrew Sonnenschein (poster session) SLAC Summer Institute

  18. Liquid Xenon Also a scintillator (Spooner) 10-20keV (50-100 keV ER) e- recoils from ’s Nuclear recoils From neutrons ’s 1 10 100 t (ns) Distinct Quantities to Measure • 1) Time Structure of the Pulse • 2) Pulse Height/Area via: • Ionization (like Ge) • Scintillation (like NaI) • Heat/Phonons • Physical Size of Ionization NaI NaI DAMA does not use this ER: 130-150 KeV (I) t Gerbier et al., 1998 Width of pulse SLAC Summer Institute

  19. to electrons to electrons Distinguishing Nuclear Recoil • Nuclear recoil energy lost mainly to collisions with other nuclei • Nuclear recoils deposit lots of energy in lattice excitations: phonons... heat • Nuclear motion poor at causing electronic excitation, ionization SLAC Summer Institute

  20. Simultaneous Measurement of Phonons(Heat) + Ionization • Temperature-20 mK • D(Temp)/D(Energy) • D(Temp)NTD Ge • Slow (10’s ms) • Ionization - E applied Edelweiss E • Background (e- from ) … strong ionization signal… equal phonon signal (!) • Nuclear recoil… reduced (by 1/4) ionization signal, strong phonon signal SLAC Summer Institute

  21. Slope really 1! Ionization Phonons Egap = 3/4 eV w = 3 eV Separation of Nuclear Recoil from e- Recoil Nuclear recoils (induced by a neutron source) Electron recoils (induced by a  source) =1 (bkgd) 1/3 (sig) Shutt et al., 1992 SLAC Summer Institute

  22. Edelweiss (depth: 4500 mwe) 0.32 kg/ Ge detector Roman Lead 3×0.32kg Germanium Detectors L. Chabert, EPS `03 Aachen SLAC Summer Institute

  23.   Edelweiss Data: ’s Suppressed by 1000 Bolometer 1 Bolometer 2 Bolometer 3 • 10.86 kg.d (fiducial) • Good phonon channel 300 eV (FWHM) resolution during most of the runs • Noisy charge channel • 30 keV threshold • 7.51 kg.d exposure (fiducial volume) • Best charg. channel : 1 keV (FWHM) • 20 keV threshold • 3.72 kg.d (fiduc.) • Smaller exposure due to electronics problems • 30 keV threshold L. Chabert, EPS `03 Aachen SLAC Summer Institute

  24. External  Ionization electrons get trapped in this electrode Electrode Implants z Those electrons never drift over to the other electrode… ionization signal reduced… but, all the phonons/heat still present… (ionization)/(phonons) < 1  E CDMS effort: measure z Betas... Germanium SLAC Summer Institute

  25. Edelweiss and other’s results CDMS no background subtraction hep-ex/0306001 28 kg-days (Ge, phonon/ion.) CDMS with background subtraction hep-ex/0306001 28 kg-days (Ge, phonon/ion.) DAMA/Edelweiss inconsistent at 99.9%... ZEPLIN I (preliminary) 230 kg-days (Liq Xe) ... not accounting for differential systematics EDELWEISS 2003 no background subtraction 31 kg-days (Ge, phonon/ion.) L. Chabert, EPS `03 Aachen SLAC Summer Institute

  26. m m n CDMS: not as deep… neutron background 17 mwe Active Muon Veto Pb Shield Copper n n Fridge Inner Pb shield Polyethylene Detectors ... Experiment moved to Soudan, 2100 mwe depth R. Schnee SLAC Summer Institute

  27. 1/5000 ’s misid’ed as nuclear recoils FET cards SQUID cards • Surface electrons • Z1 ()or Z5 (+) 4 K 0.6 K 0.06 K 0.02 K Nuclear Recoils ZIP 1 (Ge) ZIP 2 (Ge) ZIP 3 (Ge) ZIP 4 (Si) ZIP 5 (Ge) ZIP 6 (Si) CDMS Layout, Data 8 cm 4 Germanium Detectors (0.66 kg total) 2 Silicon Detectors (0.2 kg total)  Small DM rate, high neutron rate R. Schnee SLAC Summer Institute

  28. Al ~ 10mK RTES () 4 3 2 1 normal T (mK) Tc ~ 80mK superconducting Technology of `ZIP’s (Z for z) Very different from Edelweiss, although the objective is the same… the `phono-cathode’ quasiparticle trap W Transition-Edge Sensor (TES) Al Collector quasiparticle diffusion Cooper Pair Si or Ge phonons • Signal much faster - microseconds • 3-d imaging (Z) R. Schnee SLAC Summer Institute

  29. The ZIP Phono`cathode’... 380mx60maluminum fins 1mtungsten • 4 segments + timing to get x,y on the face • rise time to get z, into the face R. Schnee SLAC Summer Institute

  30. Surface-electron recoils (selected via nearest-neighbor multiple scatters from 60Co source) (Single-scatter) photons from 60Co Source Neutrons from 252Cf source Accept Reject ZIP Surface Electron Rejection Surface electrons still likely to be the limiting background R. Schnee SLAC Summer Institute

  31. 0.00014 a bit dated;  now X10 better, surface electron X2 better 0.0005 0.00074 CDMS Expected Background Levels In DRU, ev/kg/kev/day 0.0024 CDMS-II Proposal SLAC Summer Institute

  32. Catalog of Recoil Experiments Rick Gaitskell SLAC Summer Institute

  33. Future Performances Rick Gaitskell SLAC Summer Institute

  34. Prognostication SLAC Summer Institute

  35. A Proposal… 5 billion years ago…(indirect DM detection) Get 1057 protons in a sphere (ignite to enable a neutrino program) Wait for WIMPs to collect (spin-dependent cross section - proton’s spin) Detect on a nearby iron ball via the annihilation of WIMPs (with themselves) to neutrinos Review Panel’s Recommendations/Queries: 1)What if WIMP’s don’t self annihilate… no answer 2) Hey, you’re `iron ball’ is great for collecting WIMPS via spin-independent scattering, since A of Iron is big (54)! (thanks) 3) Funding for preliminary studies... SLAC Summer Institute

  36. Study Results... For SUSY WIMPs… 1) Sun, rate bottleneck is capture not annihilation 2) Earth, situation reversed 3) `Relative Efficiency’ function of WIMP mass Earth… best when WIMP mass same as Iron mass… same reason hydrogen is the best neutron moderator Sun lower masses… little capture SLAC Summer Institute

  37. Solar/Earth Comparison (WIMP models for spin/scalar comparison) Annihilation Rate in Earth is Earth Bottleneck (for detector on Earth) Capture Rate in Earth is Earth Bottlneck SLAC Summer Institute

  38. Super-Kamiokande’s Results... Upward going muons Desai, IDM 02 SLAC Summer Institute

  39. Transcribe to the Direct Detection Plot Model dependent… but less so than I thought. Spin-dependent (Sun) Scalar (Earth) Desai, IDM 02 SLAC Summer Institute

  40. Future Indirect Detectors (neutrino) Feng, Matchev, Wilczek 2000 SLAC Summer Institute

  41. Cosmic Positrons - Halo WIMP annililation HEAT… terrific balloon experiment… saw an excess Edsjo, IDM 02 SLAC Summer Institute

  42. Positron Future… ’s too Feng, Matchev, Wilczek 2000 SLAC Summer Institute

  43. 1021 1018 1015 1012 109 106 m (GeV) 103 1 10-3 10-6 10-9 Milli-CHAMP Limits Excluded Regions Overclose Universe (Thermal) Charge Fraction SLAC Summer Institute Davidson, Hannestad, Raffelt, hep-ph/0001179

  44. Stable CHAMPs in Matter DM, stop in earth Perl et al., hep-ph/0102033 SLAC Summer Institute

  45. Some conclusions • Rutherford/Chadwick hunted neutron for 12 years • Hints first seen on continent, interpreted as photons… • Neutrino studies started about 90 years ago… • Masses? Majorana? Still not fully nailed down... • Dark Matter… • Prepare for a long ride… no physical law guarantees that discoveries happen within any human’s lifetime • The only guarantee: if we fail to look, we will fail to find. SLAC Summer Institute

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