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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) 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? • 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
2 vDM1/2 =0 km/s vDM1/2 300 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
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
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
0.01950.031 -0.00010.019 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
DAMA noise... >1 pe threshold <10-4 cpd... SLAC Summer Institute
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
Halo Variation Kamionkowski and Kinkhabwala (1997) SLAC Summer Institute
A2 2 J(J+1) J0 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… np) LIBRA 250kg, NAIAD continues, ANAIS in Spain... SLAC Summer Institute
Background Electron Recoils Er v/c 0.3 Sparse Energy Deposition Discrimination of Recoils Signal Nucleus Recoils Er v/c 710-4 Dense Energy Deposition v/c small; Bragg 0 Differences the Basis of Discrimination SLAC Summer Institute
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
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
Track Etch Detectors Struck Nucleus Corrosive Etch Mica, CR39 Large dE/dx Ancient Mica 0.5109 yr Exposure fraction mm2 area 100 Å http://moedal.web.cern.ch/moedal/moedal_track.htm SLAC Summer Institute
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
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
Lose the Gelatin… get all Target Really a bubble chamber... CF3Br Juan Collar and Andrew Sonnenschein (poster session) SLAC Summer Institute
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
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
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
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
Edelweiss (depth: 4500 mwe) 0.32 kg/ Ge detector Roman Lead 3×0.32kg Germanium Detectors L. Chabert, EPS `03 Aachen SLAC Summer Institute
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
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
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
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
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
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
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
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
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
Catalog of Recoil Experiments Rick Gaitskell SLAC Summer Institute
Future Performances Rick Gaitskell SLAC Summer Institute
Prognostication SLAC Summer Institute
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
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
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
Super-Kamiokande’s Results... Upward going muons Desai, IDM 02 SLAC Summer Institute
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
Future Indirect Detectors (neutrino) Feng, Matchev, Wilczek 2000 SLAC Summer Institute
Cosmic Positrons - Halo WIMP annililation HEAT… terrific balloon experiment… saw an excess Edsjo, IDM 02 SLAC Summer Institute
Positron Future… ’s too Feng, Matchev, Wilczek 2000 SLAC Summer Institute
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
Stable CHAMPs in Matter DM, stop in earth Perl et al., hep-ph/0102033 SLAC Summer Institute
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