The Search for Dark Matter with the XENON Experiment

Transcription

1 The Search for Dark Matter with the XENON Experiment Elena Aprile Columbia University Paris TPC Workshop December 19, 2008

2 World Wide Dark Matter Searches Yangyang KIMS Homestake LUX SNOLAB DEAP/CLEAN PICASSO Boulby ZEPLIN DRIFT Kamioka XMASS Soudan CDMS Frejus/ Modane EDELWEISS Canfranc ANAIS NEXT ArDM Gran Sasso CRESST DAMA/LIBRA WARP XENON 2

3 Why Liquid Xenon for Dark Matter Detection WIMP Scattering Rates R M det M χ ρσ v Rate [evts/kevr/kg/day] evts/0-kg/year (E th =5 kevr) 8 evts/0-kg/year (E th =15 kevr) Xe (A=131) Ge (A=73) Ar (A=40)! Large A (~ 131) good for SI!~ A 2 if low Eth! 129 Xe (26.4%) & 131 Xe (21.2%) good for SD!! No radioactive isotopes (Kr85 can be removed)! High stopping power (Z=54, "=3 g/cc)! Efficient and fast scintillator (~ 80% of NaI)! Good ionization yield (W=15.6 ev)! Modest quenching factor for NR ( ) -6! Background Rejection: Charge and Light detection (> 99.5%) plus 3D localization and self-shielding M χ = 0 GeV, σ χ p = 45 cm 2! Easy cryogenics at ~165K! Inert, not flammable, very good dielectric Recoil Energy [kevr]! Modest cost for large mass detector 3

4 The XENON two-phase TPC concept WIMPs/Neutrons Top PMT Array nuclear recoil Gammas electron recoil 4

5 The XENON Dark Matter Search Phases the past ( ) the current ( ) the future ( ) XENON Achieved (2007)!SI=8.8 x -44 cm 2 XENON0 Projected (2009)!SI~2x -45 cm 2 XENON1T Projected (2014)!SI~ -47 cm 2 5

6 XENON WIMP-Nucleon Cross-Section Upper Limits Spin-independent Phys. Rev. Lett. 0, (2008) Spin-dependent Phys. Rev. Lett. 1, (2008) CDMS II XENON CDMS ZEPLIN-II XENON (NO BKG SUBTRACTION) 8.8 x -44 cm 2 at 0 GeV 4.5 x -44 cm 2 at 30 GeV Constrained Minimal Supersymmetric Model (NO BKG SUBTRACTION) 6 x -39 cm 2 at 30 GeV 6

7 The Energy Resolution of the XENON TPC Counts kev 2.6% (!/E) 583 kev 2.0% (!/E) Th-228 (with activated xenon) (single-scatter events) kev 2.0% (!/E) Xe-131m 164 kev 727 kev 1.6% (!/E) 860 kev (S2 Saturated) 2.4% (!/E) Energy [kev]

8 ..quite good for neutrinoless double beta decay of Xe-136! x 27 y, 30-0 mev 1% vs 3% 120 S2 [pe] Events/bin S1 [pe] 50 Resolution (!/E) [%] σ E E R = / E [%] 6.0[%] E/MeV σ R = E 120.0/ E [%] E = 3.8 [%] E/MeV S1 only S2 only S1&S2 combined 6 4 σ E E R = 1.4 [%] = 43.0/ E/MeV E [%] Energy [kev]

9 XENON0 A new low background TPC (0 x less than XENON) in improved shield at LNGS Top PMTs ive LXe Target Bottom PMTs Bell Grids Structure Teflon Panels with HV Racetracks Active LXe Shield 170 kg LXe (vs. 20 kg in XE); 50 kg fiducial mass (vs. 5 kg in XE). x fiducial mass low radioactivity and high QE PMTs: 242 Hamamatsu R8520 (vs. 89 in XE) low activity cryostat & inner chamber & improved shielding:0 x lower background Shield PMTs Cathode Mesh Vacuum Cryostat 9

10 XENON0: The Status TPC of Assembly XENON0: the TPC Assembly the 170 kg LXe (70 kg target) 12

11 XENON0: The PMTs 242 PMTs (Hamamatsu R Al ) 80 PMTs for bottom array (33% QE) 98 PMTs for top array (23% QE) 1 square metal channel developed for XENON Low radioactivity (<1 mbq U/Th per PMT) 64 PMTs for top/bottom/side Veto (23% QE) Top Array Bottom Array PMTs for Side & Bottom Shield PMT Base 16 11

12 XENON0: Keeping it Cold! New Cryogenics System Design Pulse Tube Refrigerator (160 W )for Xe liquefaction and gas recirculation Cooling tower with PTR is an extension of the detector cryostat, mounted outside shield Xe gas is liquefied in the tower and flows into the detector vessel via super-insulated pipe

13 XENON0 Collaboration US - Swizerland - Germany - France - Italy - Portugal -Japan An international collaboration of 46 physicists from 9 institutions 13

14 Laboratori Nazionali del Gran Sasso, Italy LNGS 1400 m Rock (30 w.m.e) XENON0 LVD ICARUS OPERA

15 XENON0 Underground at the Laboratori Nazionali del Gran Sasso LNGS: 1.4km rock (30 mwe) XENON0 XENON XENON0 outside shield XENON0 inside shield XENON 15

16 XENON0 Materials Screening for low Radioactivity Radioactivity of all materials used in XENON0 measured with a dedicated HPGe counter at LNGS 16

17 Background simulations 0.15 mbq/pmt x 242 PMTs gives 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 and simulate the expected background rate in XENON0. 17

18 Expected Background and Sensitivity Reach Z (cm) 0-5 Current XENON0: gamma bkg 50 kg 30 kg -1 ) ee (dru druee = evts/kevee/kg/day R (cm) -5 e assume cross section -44 cm 2 18

19 XENON0: Data Acqusition System 19

20 XENON0 background run data Simulation Evts/keVee/kg/day 1-1 xe0_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 XENON0 MC Background all single/multiple scattering events S1 [kevee] -2-3 single scatter only with ~46 kg fiducial mass cut 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

21 Kr removal process was finished on Sep.24. Currently we are taking data to verify the Kr concentration in Xe. Less than 50 ppt Kr/Xe expected. ~7 ppb before Kr removal process 21

22 New Photodetector for XENON: Low Radioactivity - Single Photon Counting - high QE 22

23 Proposed upgrade for XENON0 ( ) 23

24 Sensitivity Reach of the XENON0 Program ] 2 (90% C.L. upper limit) [cm "!-p XENON Sensitivity Projection - 0 GeV WIMPs Current Best Sensitivity Exposure Time with Zero Bkg [month] 1 ) 2 cm 2-44 = "!-p Expected # of WIMP Events ( -1 24

25 XENON1T Detector for pre-dusel era (before 2014) Multi-ton XENON Detector for DUSEL (beyond 2014) Explore most SUSY parameter space/ accumulate WIMP statistics New design with full coverage of ultra-low background photodetectors and cryostat Larger International Collaboration Estimated project cost: $25M (XENON1T) Multi-ton scale for DM/neutrinoless double beta decay/pp solar neutrinos $50-0M 25

26 XENON Sensitivity Goal 26

27 Summary 2008 a very good year for direct DM detection : new SI and SD results (XENON, CDMS, COUPP) Annual modulation signal re-confirmed by DAMA/LIBRA: idm scenario can reconcile it with other results 2008 also a very good year for indirect DM detection: intriguing new results from PAMELA/ATIC 2009 a crucial year for direct detection: expect new results from CDMS, XENON0, WARP, etc XENON0 operational underground: currently the largest two-phase TPC at work Data taking for Dark Matter Search will start early 2009:!SI~2x -45 cm 2 after 7 months bkg free Will be able to test both elastic and inelastic DM models with great sensitivity-annual modulation sensitive Proposed XENON0 upgrade: test key technologies for XENON1T and reach x better sensitivity International Collaboration of ~50 people from US, Switzerland, Germany, France, Portugal, Italy, Japan