1 - SLAC
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Searches for Dark Matter (the Quest) Harry Nelson UCSB 2003 SLAC Summer Insitute Aug. 5-6 2003 HNN Recap - Direct Detection UCSB How to dredge the small (0.01 DRU= ev/(kg d keV) up out of a bigger background 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 8/6/03 SLAC Summer Institute 2 HNN Annual Modulation in Rate UCSB • `Usual Simplification’: Halo particles are at rest, on average ⟨vDM⟩1/2 =0 km/s • Sun moves through Halo - `apparent’ wind • Earth modulates `wind’ velocity yearly v k = 15 km/s ⟨vDM⟩1/2 ≈ 300 km/s Fig. from DRIFT DAMA at Gran Sasso Peak-to-peak up to 40% 8/6/03 SLAC Summer Institute 3 HNN Daily Modulation in Direction UCSB • Recoiling Nucleus Follows the Initial WIMP Direction… the `wind’ • Detector gaseous to reconstruct recoil direction • DRIFT at Boulby (Spooner) Fig. from DRIFT 8/6/03 SLAC Summer Institute 4 UCSB Copper NaI Lead PMT DAMA – 100 kg of NaI PMT HNN Poly Sodium, A=23 Eobs(KeVee)≈0.25 Erecoil (KeV) Erecoil → Light Iodine, A=127 Eobs(KeVee)≈0.09 Erecoil (KeV) 8/6/03 SLAC Summer Institute 5 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 Bernabei et al., astro-ph/0307403 8/6/03 SLAC Summer Institute 6 HNN DAMA Allowed Regions (3σ) UCSB ξσp (cm2), ξ=ρ/ρ0 through 2000 10-44 10-42 Na through 2003 I Variation mainly due to changes in halo parameters 8/6/03 SLAC Summer Institute 7 HNN Halo variability UCSB Kamionkowski and Kinkhabwala (1997) 8/6/03 SLAC Summer Institute 8 HNN Perhaps WIMP couples not to nucleons, S,V,T,A,P → S,A non-relativistic but to their spin S - `nucleon’ … A - `spin’ UCSB (also, could break isospin… n≠p) A2 → Λ2 J(J+1) ξσp (cm2) 10-34 10-36 DAMA 8/6/03 SLAC Summer Institute 9 HNN Discrimination of Recoils Signal Background Nucleus Recoils Electron Recoils Er v/c ≈ 7×10-4 Dense Energy Deposition v/c small; Bragg χ0 8/6/03 UCSB γ Er v/c ≈ 0.3 Sparse Energy Deposition Differences the Basis of Discrimination SLAC Summer Institute 10 HNN Simulation (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 8/6/03 SLAC Summer Institute 11 HNN dE/dx for different recoils UCSB 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. 8/6/03 SLAC Summer Institute 12 HNN UCSB Track Etch Detectors Mica, CR39 Struck Nucleus Corrosive Etch Large dE/dx Ancient Mica 0.5×109 yr Exposure fraction mm2 area 100 Å http://moedal.web.cern.ch/moedal/moedal_track.htm 8/6/03 SLAC Summer Institute 13 HNN Mica Result UCSB Snoden-Ifft, Freeman, Price (1994) 58% 16O 16% 28Si 12% 27Al 5% 39K ξσp (cm2) ≈10-37cm2 SD: 10-33cm2 8/6/03 SLAC Summer Institute 14 HNN UCSB Superheated Droplet Detector (SDD) Target, C2ClF5 (Liquid): Temp. > Boiling Gelatin 15 gm 10 µm Collar et al., (2000) 8/6/03 χ0 Spin Dependent SLAC Summer Institute 15 HNN UCSB Distinct Quantities to Measure 1) Time Structure of the Pulse 2) Pulse Height/Area via: a) Ionization (like Ge) b) Scintillation (like NaI) c) Heat/Phonons d) 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 8/6/03 Width of pulse SLAC Summer Institute 10 10 pulse time constant ns ⟨t⟩ (ns) 100 100 16 HNN Distinguishing Nuclear Recoil z Nuclear recoil energy lost mainly to collisions with other nuclei ⟩ z to electrons 8/6/03 UCSB Nuclear recoils deposit lots of energy in lattice excitations: phonons... heat Nuclear motion poor at causing electronic excitation, ionization to electrons SLAC Summer Institute 17 HNN UCSB Simultaneous Measurement of Phonons(Heat) + Ionization Edelweiss z Temperature-20 mK ⟩ E z z z ∆(Temp)→NTD Ge ⟩ z ∆(Temp)/∆(Energy) Slow (10’s ms) Ionization - E applied Background (e- from γ) … strong ionization signal… equal phonon signal (!) Nuclear recoil… reduced (by 1/4) ionization signal, strong phonon signal 8/6/03 SLAC Summer Institute 18 HNN Separation of Nuclear Recoil from e- Recoil Nuclear recoils (induced by a neutron source) UCSB Electron recoils (induced by a γ source) Slope really 1! Shutt et al., 1992 8/6/03 SLAC Summer Institute 19 HNN Edelweiss (depth: 4500 mwe) 0.32 kg/ Ge detector L. Chabert, EPS `03 Aachen 8/6/03 UCSB Roman Lead 3×0.32kg Germanium Detectors SLAC Summer Institute 20 HNN Edelweiss Data: γ’s Suppressed by 1000 Bolometer 1 β Bolometer 2 7.51 kg.d exposure ● 3.72 kg.d (fiduc.) (fiducial volume) ● Smaller exposure ● Best charg. channel : due to electronics 1 keV (FWHM) problems ● 20 keV threshold ● 30 keV threshold L. Chabert, EPS `03 Aachen 8/6/03 Bolometer 3 β ● SLAC Summer Institute UCSB β 10.86 kg.d (fiducial) ● Good phonon channel 300 eV (FWHM) resolution during most of the runs ● Noisy charge channel ● 30 keV threshold ● 21 HNN Edelweiss and other’s results UCSB 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%... ... not accounting for differential systematics ZEPLIN I (preliminary) 230 kg-days (Liq Xe) EDELWEISS 2003 no background subtraction 31 kg-days (Ge, phonon/ion.) L. Chabert, EPS `03 Aachen 8/6/03 SLAC Summer Institute 22 HNN CDMS: not as 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 R. Schnee 8/6/03 SLAC Summer Institute 23 HNN CDMS Layout, Data FET cards UCSB 1/5000 γ’s misid’ed as nuclear recoils 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 Nuclear Recoils 4 Germanium Detectors (0.66 kg total) 2 Silicon Detectors (0.2 kg total) → Small DM rate, high neutron rate R. Schnee 8/6/03 SLAC Summer Institute 24 HNN UCSB Technology of `ZIP’s Very different from Edelweiss, although the objective is the same… the `phono-cathode’ quasiparticle trap W quasiparticle Transition-Edge diffusion Sensor (TES) Al Collector Cooper Pair Al Si or Ge phonons ~ 10mK R. Schnee 8/6/03 RTES (Ω) • Signal much faster microseconds • 3-d imaging (Z) 4 normal 3 2 1 superconducting SLAC Summer Institute Tc ~ 80mK T (mK) 25 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 R. Schnee 8/6/03 SLAC Summer Institute 26 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 Reject R. Schnee 8/6/03 SLAC Summer Institute 27 HNN CDMS Expected Background Levels UCSB In DRU, ev/kg/kev/day 0.00014 0.0005 a bit dated; γ now X10 better, surface electron X2 better 0.00074 0.0024 CDMS-II Proposal 8/6/03 SLAC Summer Institute 28 HNN Catalog of Recoil Experiments UCSB Rick Gaitskell 8/6/03 SLAC Summer Institute 29 Future Performances UCSB Rick Gaitskell HNN 8/6/03 SLAC Summer Institute 30 HNN Prognostication 8/6/03 SLAC Summer Institute UCSB 31 HNN A Proposal… 5 billion years ago… UCSB (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 is big! (thanks, review panel) 3) Funding for preliminary studies... 8/6/03 SLAC Summer Institute 32 HNN UCSB 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 lower masses… little capture 8/6/03 Sun SLAC Summer Institute 33 Solar/Earth Comparison (for detector on Earth) HNN 8/6/03 UCSB (WIMP models for spin/scalar comparison) Annihilation Rate in Earth is Earth Bottleneck Capture Rate in Earth is Earth Bottlneck SLAC Summer Institute 34 HNN Super-Kamiokande’s Results... UCSB Upward going muons Desai, IDM 02 8/6/03 SLAC Summer Institute 35 HNN Transcribe to the Direct Detection Plot UCSB Model dependent… but less so than I thought. Spin-dependent (Sun) Scalar (Earth) Desai, IDM 02 8/6/03 SLAC Summer Institute 36 HNN Future Indirect Detectors (neutrino) UCSB Feng, Matchev, Wilczek 2000 8/6/03 SLAC Summer Institute 37 HNN UCSB Cosmic Positrons - Halo WIMP annililation HEAT… terrific balloon experiment… saw an excess Edsjo, IDM 02 8/6/03 SLAC Summer Institute 38 HNN Positron Future… γ’s too UCSB Feng, Matchev, Wilczek 2000 8/6/03 SLAC Summer Institute 39 HNN 1021 1018 Milli-CHAMP Limits UCSB 1015 1012 Excluded Regions m (GeV) 109 106 103 Overclose Universe (Thermal) 1 10-3 10-6 10-9 8/6/03 Davidson, Hannestad, Raffelt, hep-ph/0001179 SLAC Summer Institute Charge Fraction 40 HNN UCSB Stable CHAMPs in Matter DM, stop in earth Perl et al., hep-ph/0102033 8/6/03 SLAC Summer Institute 41 HNN z Some conclusions Rutherford/Chadwick hunted neutron for 12 years ⟩ z Hints first seen on continent, interpreted as photons… Neutrino studies started about 90 years ago… ⟩ z UCSB Masses? Majorana? Still not fully nailed down Dark Matter… ⟩ ⟩ 8/6/03 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 42
