Shedding Light on Dark Matter from Deep Underground with XENON Kaixuan Ni (Columbia) University of Maryland, 11-25-2008
A well-known mystery for astronomers Fritz Zwicky, The Astrophysical Journal, 85 (1937) 217... All curves show a fairly rapid velocity rise to V ~ 125 km s -1 at R ~ 5 kpc, and a slower rise thereafter. Most rotation curves are rising slowly even at the farthest measured point. Neither high nor low luminosity Sc galaxies have falling rotation curves. Sc galaxies of all luminosities must have significant mass located beyond the optical image.... 2
Modern Precision Cosmology 3
Dark Matter is a stable, neutral, and heavy particle that interacts very weakly, or only through gravity. Leading DM candidates, such as neutralinos and axions, are from theories beyond the Standard Model!
Three ways to probe the nature of dark matter Indirectly search for DM annihilation products (gamma rays, neutrinos, electrons, positrons, etc.) Produce dark matter in the Collider Directly detect DM interacting with a terrestrial target 5
A fruitful year for indirect DM searches Observation of an anomalous positron abundance in the cosmic radiation [arxiv:0810.4995] PAMELA 6
A fruitful year for indirect DM searches An excess of cosmic electrons. ATIC DM local density 0.43 GeV/cm 3 Kaluza-Klein mass 620 GeV Annihilation rate 10-23 cm 3 /s J Chang et al. Nature 456, 362-365 (2008) doi:10.1038/nature07477 7
Dark Matter Equation of State dn χ dt +3Hn χ = σ A v [ (n χ ) 2 ( n eq ) ] 2 χ Ω χ h 2 = m χn χ ρ c = 3 10 27 cm 3 /s σ A v freezout σ A v freezout =3 10 26 cm 3 /s 8
A fruitful year for indirect DM searches ATIC Kaluza-Klein mass 620 GeV Annihilation rate 10-23 cm 3 /s J Chang et al. Nature 456, 362-365 (2008) doi:10.1038/nature07477 A boost factor of ~200 is required 9
Also a busy year for direct DM searches in the summer, moving against wind WIMP wind expect an annual modulation in signal! in the winter, moving away from wind
Also a busy year for direct DM searches in the summer, moving against wind WIMP wind expect an annual modulation in signal! in the winter, moving away from wind 10
Also a busy year for direct DM searches in the summer, moving against wind WIMP wind expect an annual modulation in signal! in the winter, moving away from wind DAMA/LIBRA reconfirmed their early observation of annual modulation signal [arxiv:0804.2741] 10
Also a busy year for direct DM searches DAMA allowed CDMS further improves Spin-Independent after XENON10 [arxiv:0802.3530] 11
Also a busy year for direct DM searches XENON10 Spin-Dependent pure-neutron coupling [PRL 101, 091301 (2008)] COUPP further improves Spindependent proton coupling [Science 319:933-936,2008] 12
arxiv:0810.0713
arxiv:0810.0713
arxiv:0810.0713
Are we at the edge of uncovering the nature of DM?
Direct Dark Matter Detection Galactic WIMP Halo (ρ = 0.3 GeV/cm 3 ) <V> = 220 km/s Elastic Scattering Target Nucleus Recoil Nucleus ~10-100 kev or less σ -p can be as low as 10-46 cm 2 Goodman and Witten, coherent scattering for WIMPs Phys Rev D 31, 3059 (1985) 15
The Challenges for Direct DM Detection WIMP Scattering Rates R M det M χ ρσ v Rate [evts/kevr/kg/day] -5 10 18 evts/100-kg/year (E th =5 kevr) 8 evts/100-kg/year (E th =15 kevr) Xe (A=131) Ge (A=73) Ar (A=40) large mass (ton scale) low energy threshold (a few kev) background suppression deep underground -6 10 M χ = 100 GeV, σ χ p = 10 45 cm 2 passive shield low intrinsic radioactivity 10-7 0 10 20 30 40 50 60 70 80 Recoil Energy [kevr] gamma background discrimination 16
Why do we need go to deep underground? 17
Why do we need go to deep underground? Homestake muon induced neutron flux Mei and Hime, PRD (2006) 17
Why do we need go to deep underground? 100 GeV WIMPs, 10-46 cm 2 Homestake muon induced neutron flux signal/background event rates Mei and Hime, PRD (2006) 17
World Wide Dark Matter Searches Yangyang KIMS Homestake LUX SNOLAB DEAP/CLEAN PICASSO Boulby ZEPLIN DRIFT Kamioka XMASS Soudan CDMS Frejus/ Modane EDELWEISS Gran Sasso CRESST DAMA/LIBRA WARP XENON 18
Dark Matter physicists
Dark Matter physicists Cryogenic (CDMS etc.)
Dark Matter physicists Noble Liquids (XENON etc.) Cryogenic (CDMS etc.)
The Merits of Noble Liquids for Dark Matter Detection scalability : relatively cheap and easy cryogenics at 170 K (LXe), 87 K (LAr) bkg reduction: via self-shielding low threshold : high scintillation yield gamma rejection: electron and nuclear recoil discrimination 175nm Ionisation Electron/nuclear recoil wavelength depends on gas e.g. Xe 175nm Ar 128nm Excitation Triplet 27ns Xe * Xe 2 * +Xe Singlet 3ns Xe 2 + Xe ** + Xe 175nm Recombination depends on type of recoils (stronger for nuclear recoils) Xe + +Xe +e - (recombination) Nigel Smith, RAL 2Xe 2Xe time constants depend on gas e.g. Xe 3/27ns Ar 10/1500ns 20
The Noble Liquid Revolution Noble liquids (LAr, LXe) are relatively inexpensive, easy to scale up Self-shielding reduce external background Excellent gamma background rejection (pulse-shape, or ionization/scintillation) XMASS 800-kg Single Phase (XMASS, CLEAN/DEAP) WARP Two Phase (XENON,LUX,ZEPLIN II/III,WARP,ArDM.) 21
Two-phase Xenon Detectors for Dark Matter Detection WIMPs/Neutrons Top PMT Array nuclear recoil Gammas electron recoil 22
Signals from XENON10 S1 S2 S1 S2 23
The Phased XENON Program XENON R&D (2001-2005) XENON10 (2006-2007) XENON100 (2007-2012) XENON1T (2012) 24
XENON10 WIMP Search Data 136 kg-days Exposure= 58.6 live days x 5.4 kg x 0.86 (ε) x 0.50 (50% NR) (data collected between Oct.2006 and Feb.2007) ~1800 events Statistical leakage from electron recoil band Anomalous events due to non-active Xe 4.5 27 kevr noise event WIMP Search Window 25
XENON10 WIMP-Nucleon Cross-Section Upper Limits Spin-independent Phys. Rev. Lett. 100, 021303 (2008) Spin-dependent Phys. Rev. Lett. 101, 091301 (2008) CDMS II XENON10 CDMS ZEPLIN-II XENON10 (NO BKG SUBTRACTION) 8.8 x 10-44 cm 2 at 100 GeV 4.5 x 10-44 cm 2 at 30 GeV Constrained Minimal Supersymmetric Model (NO BKG SUBTRACTION) 6 x 10-39 cm 2 at 30 GeV 26
Can XENON10 anomalous events be explained by idm? inelastic Dark Matter (idm) Spencer Chang, Graham D. Kribs, David Tucker-Smith, Neal Weiner [arxiv:0807.2250] No longer elastic scattering. If dark matter can only scatter off of a nucleus by transitioning to an excited state, the kinematics are changed dramatically δ 1 2 µβ2 c 2 100 kev µ = M χm N M χ + M N 27 N. Weiner
must have enough kinetic energy to scatter visible to DAMA and XENON visible to f(v) CDMS and WARP modulation is also significantly enhanced N. Weiner
Spectrum is dramatically modified Standard WIMPs have a spectrum that peaks at low energies
XENON10 background data adjusted for efficiencies (taking unpublished acceptance x efficiency = 0.3, error bars estimated) M χ =100 GeV, δ=0 kev, normalized to inelastic XENON10 signal M χ =100 GeV, δ = 120 kev, normalized to DAMA 2-6 kev
31 12 XENON100: The Status TPC of Assembly XENON100: the TPC Assembly the 170 kg LXe (70 kg target)
XENON100 Collaboration An international collaboration of 46 physicists from 9 institutions 32
Laboratori Nazionali del Gran Sasso, Italy LNGS 1400 m Rock (3100 w.m.e) XENON100 LVD ICARUS OPERA
XENON100 Underground at the Laboratori Nazionali del Gran Sasso LNGS: 1.4km rock (3100 mwe) XENON100 XENON10 XENON100 outside shield XENON100 inside shield XENON10 34
35 16 XENON100: The PMTs 242 PMTs (Hamamatsu R8520-06-Al ) 1 square metal channel developed for XENON Low radioactivity (<1 mbq U/Th per PMT) 80 PMTs for bottom array (33% QE) 98 PMTs for top array (23% QE) 64 PMTs for top/bottom/side Veto (23% QE) Bottom Array Top Array PMTs for Side & Bottom Shield PMT Base
Ultra-low radioactive material selection All materials used in XENON100 detector were selected based on low radioactivity 36
Background simulation 0.15 mbq/pmt x 242 PMTs gives 3000 238 U decays/day Each 238 U decay produces 15 gammas and 9 alphas 16M gamma/year (alpha,n) reaction results 7 neutron/year A realistic model based on Geant4 was constructed to propagate all the gammas/neutrons to simulate the background rate. 37
Expected Background and Sensitivity Reach Current XENON100: gamma bkg druee = evts/kevee/kg/day Z (cm) 0-5 30 kg 50 kg 10-1 ) ee (dru -2 10-10 -15-3 10-20 -4 10-25 -30 0 2 4 6 8 10 12 14 R (cm) -5 10 e assume cross section 10-44 cm 2 38
XENON100: Data Acqusition System Requirements: digitize full waveform (320!s) of 242 PMTs with no deadtime and with high rate capability for calibration CAEN V1724 Flash ADC: 14bit, 100MHz circular buffer: no deadtime on board FPGA: Zero Length Encoding only relevant signal portion transferred from ADC to DAQ computer to allow faster event transfer rates >60 Hz in calibration mode 39 20
First signals from XENON100 8 Gamma Event Digitized 7 6 5 4 3 2 1 0 0 5000 10000 15000 20000 25000 30000 Top Array Gamma Event Localized 186 187 188 185 189 184 8 9 7 10 190 183 6 11 36 37 191 38 5 35 39 12 182 4 34 59 60 192 61 40 13 58 62 181 3 33 78 79 193 57 41 14 77 80 63 91 180 2 32 56 64 42 15 194 76 90 92 81 179 1 31 55 75 89 97 98 93 82 65 43 16 195 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 S1 13900 14000 14100 14200 14300 8 7 6 5 4 3 2 1 0 S2 14400 14600 14800 15000 15200 30 54 74 88 96 94 83 66 17 210 44 196 95 29 53 73 87 84 67 45 18 209 86 85 197 72 68 28 52 71 19 69 46 208 70 198 51 47 27 20 50 48 207 49 26 21 199 25 206 22 24 23 200 205 201 204 203 202 40
XENON100 background run data Simulation Evts/keVee/kg/day 1-1 10 xe100_080620_2018 edge events with poor light collection, will be removed by radial position cut all single/multiple scattering events Rate [evts/kg/day/kev] 1-1 10 XENON100 MC Background all single/multiple scattering events -2 10-2 10 single scatter only with ~46 kg fiducial mass cut -3 10 0 500 1000 1500 2000 2500 3000 S1 [kevee] -3 10 0 500 1000 1500 2000 2500 3000 E [kev] Detector has been fully filled with liquid xenon. First Measured background Spectrum in good agreement with MC prediction! WIMP search run is planned to start in April 2009. 41
A proposal to upgrade XENON100 (2009-2012) 42
Sensitivity Reach of the XENON100 Program ] 2 (90% C.L. upper limit) [cm "!-p -43 10-44 10 10-45 -46 10 XENON Sensitivity Projection - 100 GeV WIMPs Current Best Sensitivity 2009 2011-2012 0 5 10 15 20 25 30 35 40 Exposure Time with Zero Bkg [month] 10 10 1 10 ) 2 cm 2-44 = 10 "!-p Expected # of WIMP Events ( -1 43
Multi-ton scale XENON Detector for DUSEL (beyond 2012) Explore the full region/accumulate WIMP statistics New design with full coverage of ultra-low background photodetectors and cryostat Larger International Collaboration Total project cost: $50M-$100M neutrinoless double beta decay pp solar neutrinos 44