Direct Dark Matter Searches: an Overview GGI Conference on Dark Matter Florence, February 9, 2009 Laura Baudis University of Zurich 1
Goal of Direct Detection Experiments • Detect new, yet undiscovered particles, which may be responsible for the dark matter in our galaxy. Example: WIMPs = heavy (few GeV - few TeV), color and electrically neutral; in thermal equilibrium with the rest of the particles in the early universe, freeze out when M W >>T F M tot , lum ≈ 9 × 10 10 M M virial ≈ 1...2 × 10 12 M Sun ρ χ 0.3 GeVcm − 3 ρ χ 3000 WIMPs ⋅ m − 3 ( M WIMP = 100 GeV) (J. Diemand et all, Nature 454, 2008, 735-738) (Klypin, Zhao & Somerville 2002) Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 2
Strategy for WIMP Direct Detection • Elastic collisions with atomic nuclei • Rates depend on: [m χ , σ ], [f(v), ρ 0 ], [N, E th ] ... f ( = σ 0 ρ 0 dR v,t) v max ∫ 2 m χ µ 2 F 2 ( E R ) d 3 v v> m N E R /2 µ 2 Differential rates for different targets (SHM) dE R v ] ) V e k d g • with WIMP-nucleon cross sections k M WIMP = 100 GeV ( / s σ WN =4 × 10 -43 cm 2 < 10 -7 pb, the expected rates are t n e v e [ < 1 event/100kg/day e t a r . f f i • Energy of recoiling nuclei D 2 = µ 2 v 2 q E R = (1 − cos θ ) ≤ 50 keV Recoil energy [keVr] 2 m N m N Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 3
A Dark Matter Disk in The Milky Way • from Λ CDM numerical simulations which include the influence of baryons on the dark matter [J. I. Read, G. Lake, O. Agertz, V. P . Debattista, MNRAS 389, 1041, 2008] • the stars and gas significantly alter the local phase space density of dark matter ➡ stars and gas settle onto the disk early on (z=1), affecting how smaller dark matter halos are accreted ➡ the largest satellites are preferentially dragged towards the disk by dynamical friction, then torn apart ➡ the material from the satellites settles into a thick disk of stars, and dark matter ➡ the dark matter density in the disk is constrained to about 0.25 - 2 x halo density in Earth frame dark disk halo thin disk thick stelar disk Read, Lake, Agertz, Debattista, MNRAS 389, 1041, 2008 Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 4
A Dark Matter Disk in The Milky Way • The solar system is embedded into the macroscopic structure of the dark disk δ = ρ Disk ≤ 2 • the local density is constrained by ρ SHM v disk = [0,50,0] km ⋅ s − 1 ; σ disk = 50 km ⋅ s − 1 • the velocities and dispersions are taken as ➡ the dark disk increases the rates at low recoil energies and provides and modifies the shape of the recoil spectrum, depending on the WIMP mass Recoil energy below which the signal is dominated by the dark disk Xenon Germanium XENON10 threshold T. Bruch, J. Read, LB, G. Lake, APJ in press XENON10 threshold Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 5
Direct Detection Techniques LiF, Al 2 O 3 WIMP WIMP Phonons CaWO 4, Ge, Si Al 2 O 3 Charge E R Light NaI, CsI Ge, CS 2, CF 4 LAr, LNe, LXe LAr, LXe In this talk: only recent results (2007-2008) and status of near future projects Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 6
DAMA: NaI Experimental Results KIMS: CsI CDMS-II 73 Ge Spin-independent cross section (normalized to nucleons) XENON10: 129 Xe ] 2 m DAMA/ c LIBRA [ SI S σ p CMSSM EDELWEISS: 2005 n i o n e - l WARP: 2007 c d u e n - p P M e CRESST: 2008 I n DAMA: NaI W d e ZEPLIN III: 2008 n XENON10: 129 Xe t CDMS: 2008 COUPP KIMS: CsI XENON10: 2007 CMSSM2008 SuperK (Roszkowski, Ruiz, Trotta) WIMP Mass [GeV] CMSSM Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 7
DAMA/LIBRA 2008 • modulation of event rate confirmed in 2008 • 25 NaI detectors a 9.7 kg; each viewed by 2 PMTs (5.5-7.5 p.e./keVee) • 4 years of data taking: 192 x 10 3 kg days residuals from average rate dR ( ) ≈ S 0 ( E ) + S m ( E )cos ω ( t − t 0 ) dE E , t t 0 = 152.5 d T = 1 year S m = (0.0215 ± 0.0026) counts/(day kg keV) Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 8
DAMA/LIBRA 2008 signal in region dominated by PMT noise (does the tail of the noise distribution modulate?) single hit all event spectrum signal very close to threshold modulation of a peak around 3 keV? what is the contribution of the 40 K 3 keV X-ray in the singles spectrum? no modulation above 6 keV S m event spectrum modulation amplitude co-added over detectors A=(0.9±1.1) 10 -3 cpd/kg/keV Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 9
DAMA Signal and Existing Experimental Limits at Low WIMP Masses M. Fairbairn, T. Schwetz • WIMP hypothesis: severe tension with other experiments! Spin-independent DAMA with channeling arXiv:0808.0704v1 Savage, Gelmini, Gondolo, Freese Spin-dependent arXiv:0808.3607v1 Ion channeling effect: scattered ion parallel to crystal axis will undergo small-angle scattering which will channel it along the gaps in the lattice; DAMA such an ion has lower dE/dx, yielding increased with light , effectively reducing the energy threshold channeling for low-energy nuclear recoils Channeling: has not yet been demonstrated for nuclear recoils starting from a lattice site, only for incident ion beams; should be tested in dedicated experiment + many other papers.... Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 10
New Experimental Results at Low WIMP Masses TEXONO: 4 x 5 g Ge CoGeNT: 500 g PPC Ge spin-independent spin-dependent spin-independent S.T. Lin et al. 0712.1645v4 Aalseth et al. PRL 101 (2008) Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 11
Limits from indirect detection of ν ’s (SuperK) Spin-dependent Spin-independent Hooper, Petriello, Zurek, Kamionkowski, arXiv:0808.246v4 Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 12
The COUPP Experiment • superheated liquid -> detects single bubbles induced by high dE/dx nuclear recoils; advantage: large masses, low costs, SD, SI (I, Br, F , C), high spatial granularity, ‘rejection’ of ERs 10 10 at 10keV r ; challenge: reduce alpha background • n-induced 2 kg detector at 300 mwe in 2006: α BG from walls event 222 Rn decays -> 210 Pb plate-out + 222 Rn emanation (multiple run with 2 kg in 2007/2008 (reduced backgrounds) scatter) 60 kg module under construction at FNAL -> 3 x 10 -8 pb WIMP: spin-dependent single scatter Behnke, Collar et al., Science 319 (2008) Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 13
CDMS Results from the Soudan Mine • 30 Ge (4.75 kg) and Si (1.1 kg) detectors at ~ 20 mK in 5 towers • Run 123+124: 163 live days, results published in PRL102 (2009) 011301 • Run 125-128: 240 live days under analysis, first results in summer 09 (sensitivity reach ~ 1x10 -44 cm 2 ) 1.5 1 Ionization yield Ge: 121.3 kg d (after cuts) 0.5 zero events ZEPLIN III 2008 0 0 20 40 60 80 100 CDMS 2009 Recoil energy (keV) PRL102 (2009) 011301 XENON10 2007 Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 14
Cryogenic mK Experiments: Near Future CRESST at LNGS EDELWEISS at LSM CDMS/SuperCDMS at Soudan 10 kg array of 33 CaWO 4 CDMS-II run 129 in progress 10 kg (30 modules) of NTD detectors SuperCDMS detectors (1 ʼʼ thick ZIPs, and NbSi Ge detectors in new 66 SQUID channel array each 650 g of Ge) have been tested new cryostat - new limit from operating 2 Installation of first SuperTower at - new charge electrodes detectors (48 kg d) published Soudan in spring 2009 - 100 kg d under analysis in 2008, arXiv:0809.1829v1 Goal: 5 x 10 -45 cm 2 with 16 kg Ge - data taking in progress - new run in progress Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 15
Noble Liquids Time Projection Chambers Ar (A = 40); λ = 128 nm Xe (A=131); λ = 175 nm • Dense, homogeneous targets/detectors; high light and charge yields • Prompt (S1) light signal after interaction in active volume; charge is drifted, extracted into the gas phase and detected as proportional light (S2 ) gamma S2 E ext h ν Gas S1 h ν drift time Liquid E d t drift h ν WIMP (here neutron) e - E R h ν S2 S1 drift time Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 16
The XENON10 Experiment at LNGS • 22 kg LXe (15 kg in active volume) • 89 1’’x 3.5cm R8520 PMTs, in 2 arrays ➡ x-y position from PMT hit pattern; σ x-y ≈ 1 mm ➡ z-position from ∆ t drift (v d , e- ≈ 2mm/µs), σ Z ≈ 0.3 mm • backgrounds: dominated by detector materials, well understood Monte Carlo Data simulation Most background events at boundaries Fiducial mass: 8.9 kg LXe Laura Baudis, University of Zurich, GGI Dark Matter Conference, February 9, 2009 17
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