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Experimental dark matter searches

Experimental dark matter searches. Weakly Interacting Massive Particles. A WIMP c is like a massive neutrino: produced when T >> m c via annihilation through Z (+ other channels); annihilation/pair creation maintain thermal equilibrium

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Experimental dark matter searches

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  1. Experimental dark matter searches

  2. Weakly Interacting Massive Particles A WIMP c is like a massive neutrino: produced when T >> mc via annihilation through Z (+ other channels); annihilation/pair creation maintain thermal equilibrium If interaction rates high enough, the density drops as exp(- mc/T) as T drops below mc: annihilation continues, production becomes suppressed • But, weakly interacting •  may freeze out • before total annihilation if • > Gann~ nc ann v • i.e., if annihilation too slow to keep up • with Hubble expansion • Leaves a relic abundance: • ch210-27 cm3 s-1 ann v freeze out  if mc and ann determined by electroweak physics, thenc~ 1

  3. m nm Detecting WIMPs 0 • Direct detection: • WIMPs elastically scatter off nuclei nuclear recoils • Measure recoil energy spectrum in target • Indirect detection: • WIMPs annihilate • in halo: e+, p, g • in Sun, Earth core: high energy n’s  v/c  10-3 0

  4. c c c c ~ q H,h,Z q q q q Ge Si I/Xe Direct detection • WIMPs elastically scatter off nuclei in targets, producing nuclear • recoils, with nc related to ann • (same diagrams - via Z, h, H, and squarks) • Energy spectrum of recoils is exponential with E ~ 50 keV, • dependent on WIMP and target nucleus masses: Boltzmann • distribution (isothermal halo) + s-wave scattering (NR) WIMP flux Amplitude of recoil energy spectrum, i.e. event rate, normalized by nc, local WIMP number density, and nucleus-dependent A2F2 (Q) s-wavescattering Elastic ScatteringForm Factors At low Q, scattering is coherent and ~A2. Coherence lost as Q increases; parameterized by form factor.

  5. WIMP nucleus cross section • In MSSM/CMSSM (neutralino): in general: s: 10-5 between and 10-11 pb sensitivity of current experiments: ~ 10-6 pb testing some models, will test more models in future as sensitivity improves Accelerator constraints shrink SUSY bounds: mainly constrained upper bound g-2 can provide constraint on lower bound if tentative disagreement due to SUSY 1 event kg-1 d-1 current experiments 1 event 100 kg-1 yr-1 detectors: low threshold low background large masses good event discrimination

  6. galactic center Sun 230 km/s Dec. v0 June Dec log dN/dErecoil June ~3% effect Erecoil WIMP signatures Annual modulation: WIMP Isothermal Halo (assume no co-rotation) v0~ 230 km/s WIMP wind Earth 30 km/s (15 km/s in galactic plane)

  7. Annual Modulation • Not distinguish between WIMP signal and background directly • From the amplitude of the modulation, we can calculate the • underlying WIMP interaction rate WIMP Signal ±2% Background Dec June Dec June Dec June Dec June

  8. WIMP signatures Diurnal modulation: v0: solar motion WIMP WIMP WIMPs 42o vo a Nuclear recoil The mean recoil direction rotates over one sidereal day The distribution of the angle a between the solar motion and recoil directions: peaks at a=180o

  9. WIMP signatures • Material dependence: • WIMPs: Gehas ~6x higher interaction rate per kg than Si • neutrons: Si has ~2x higher interaction rate per kg than Ge Background neutrons WIMPS 40 GeV

  10. Phonons ER Ionization Scintillation Direct detection techniques CRESST ROSEBUD CUORICINO CRESST II ROSEBUD CDMS EDELWEISS HDMS GENIUS IGEX MAJORANA DRIFT (TPC) DAMA ZEPLIN I UKDM NaI LIBRA XENON ZEPLIN II,III,IV Large spread of technologies: varies the systematic errors, important if positive signal! All techniques have equally aggressive projections for future performance But different methods for improving sensitivity

  11. Where do we stand? DAMA 3s ~ 1 event/kg/day Most advanced experiments start to test the predicted SUSY parameter space One evidence for a positive WIMP signal Not confirmed by other experiments CDMS EDELWEISS ZEPLIN I Predictions: Ellis, Baltz & Gondolo, Mandic & all

  12. The DAMA/LIBRA experiment LIBRA DAMA • At LNGS (3800 mwe) • 9 x 9.7 kg low activity NaI crystals, • each viewed by 2 PMs • 2 methods of backgrd discr: • PS; annual modulation • -> positive signal (4 s) • What next? • update to LIBRA (250 kg) • improved backround (~few) • improved light yield • Installation completed; • analyze additional 3 yr • of DAMA data (finished Jan 02) Day 1 = Jan 1, 1995

  13. gammas neutrons gamma source neutron source electrons The CDMS II experiment • At SUF (16 mwe) /Soudan (2030 mwe) • uses advanced athermal phonon (TES) • measuring charge and phonons • discrimination • position resolution • surface event rejection

  14. FET cards SQUID cards The CDMS II experiment • 1 tower of 4 Ge and 2 Si ZIPs • operated at SUF 2001-2002; > 120 livedays • > 99.98 % rejection of bulk electron recoils: 5-100 keV • > 99 % rejection of surface events: 10-100 keV • n background x 2.3 lower due to inner poly (as expctd); • 20 Ge recoil single scatters, 2 Si single scatters, • 2 triple scatter, 1 nnn double scatter; consistent • with all single scatters caused by neutrons • first results submitted to PRL, hep-ex/0306001 Si Ge Ge Ge Ge Si Ge Si Muon anticoincident background

  15. CDMS and DAMA • assumptions of standard halo, standard WIMP interactions • CDMS results incompatible with DAMA model-independent annual-modulation data (left) at > 99.8% CL even if all low-energy events were WIMPs predicted WIMP modulation predicted WIMP spectrum alone Best simultaneous fit to CDMS and DAMA predicts too little annual modulation in DAMA, too many events in CDMS (even for no neutron background) CDMS data neutron spectrum fit

  16. SUSY gm-2 Baltz&Gondolo, PRL 86 (2001) 5004 No SUSY gm-2 Baltz&Gondolo, PRL 86 (2001) 5004 CMSSM Ellis et al. (2001) PRD 63, 065016 The CDMS II experiment first 2 towers at the Soudan mine (2030mwe) m-flux reduced by 104, n-flux by ~ 300 first dark April 03! goal: 5 towers, 4 kg Ge, 1.5 kg Si 0.1 events/kg/keV/yr EDELWEISS CDMS 03 CDMS Soudan entrance to the mine

  17. The EDELWEISS experiment • In Frejus UL (4800 mwe); 320 g Ge crystals • measure thermal phonons + charge • EDELWEISS I: 1 kg stage • fall 2000, first semester 2002, • October 2002 - March 2003 • total exposure: • 13.8 kg  day @ Erec > 20 keV, • 30.5 kg  day @ Erec > 30 keV • Incompatibility with DAMA candidate • (99.8% C.L.) confirmed with three different • detectors and extended exposure G. Chardin 2003

  18. The EDELWEISS experiment • New run started: improved energy threshold • ≈100% detection efficiency at 10 keV ER • September 2003: • end EDELWEISS-I run • install EDELWEISS-II • 21  320 g Ge-NTD detectors • 7 thin film (NbSi) 200 g Ge detectors • Achieve factor 100 improvement • in sensitivity 100 l dilution cryostat for up to 120 detectors (36 kg Ge)

  19. The ZEPLIN I experiment • Operating at the Boulby mine (~3000 mwe) • Single phase, scintillation in LiXe, PSD • 3.7 kg liquid Xe (3.1 kg fid vol) • 1 ton liquid scintillator veto • 75 d livetime, 230 kg d of data Neutron source Gamma source 10-20keV Background: 40 dru @ 100keV implies 85Kr < 10-17 atoms/atom (standard Xe used) Fiducial Volume cut

  20. ER Ionisation Xe+ +Xe Excitation Xe2+ +e- Xe* Xe**+ Xe 175nm 175nm +Xe 2Xe 2Xe Xe2* Triplet Singlet 3ns 27ns The ZEPLIN experiment ZEPLIN II at RAL, UK ZEPLIN I Future ZEPLIN I: more data, low Kr Xenon ZEPLIN II/III: Ionization + scintillation, 2 phase Xe; 30 kg, 6kg high field II: tested at RAL, UK, PMs being produced to be installed at Boulby in 2003

  21. gamma region Gamma Region Scattered WIMP Neutron Region neutron region overlap Overlap Region CS2 Recoil CS2 Recoil Atom Electron Cathode Drift direction MWPC Readout Plane Electric Field The DRIFT experiment • In the Boulby mine (3000 mwe) • Resolve ionization tracks in a gas • TPC filled with low-pressure EN gas (CS2) • Endcap sense-planes: determination of range, • orientation & energy (via ionization) • e--capture by CS2 suppresses diffusion • during charge-drift • operates at ~40 torr , 140 g target mass • discrimination through dE/dx measrmnt • Future: DRIFT-II • scaled-up DRIFT-I with full 3D readout • & x50 sensitivity • R&D: higher-resolution readout, • higher-pressure operation • cathode-readout of positive ions • allowing event localization away • from wire planes

  22. The ‘far’ future 1 event/kg d: EDELWEISS, CDMS, ZEPLIN 1 event/kg yr: CDMSII, CRESSTII, EDELWEISSII, ZEPLINII 1 event/100 kg yr: future projects! 1 ton is needed in order to detect 10 events per year ats = 10-46 cm2 Predictions: Bottino, Ellis, Gondolo

  23. The ‘far’ future

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