Status of the XENON Dark Matter Experiment Karl Ludwig GiboniGiboni - Columbia Astrophysics Laboratory KEK Physics Seminar February 10, 2009 World Wide Dark Matter Searches Boulby SNOLAB ZEPLIN DEAP CLEAN DRIFT / PICASSO Yangyang Homestake KIMS LUX Frejus Mod / ane EDELWEIS Kamioka Soudan S Gran Sasso XMASS CDMS Canfranc CRESST ANAIS DAMA LIBR / NEXT A ArDM WARP XENON 2 XENON Collaboration 100 US Swizerland Germany France Italy Portugal - - - - - - Japan An international collaboration of physicists from institutions 46 9 3 Dark Matter Physicists vs Time Noble Liquids (XENON etc.) Cryogenic (CDMS etc.) Laboratori Nazionali del Gran Sasso, Italy LNGS 1400 m Rock (3100 w.m.e) XENON100 LVD ICARUS OPERA Xe + Ionisation +Xe Electron/nuclear recoil + Xe 2 Excitation +e - (recombination) Xe * Xe ** + Xe +Xe Xe * 175nm 2 175nm Triplet Singlet 27ns 3ns 2Xe 2Xe 6 XENON LUX ZEPLIN II III WARP ArDM XMASS CLEAN DEAP ( ,, , / , , ) ( , / ) 7 Why Noble Liquids for Dark Matter Recombination depends on type of ✦scalability relatively : recoils (stronger for inexpensive for large scale nuclear recoils) + multi ton detectors Xe ( - ) Ionisation +Xe ✦easy cryogenics K Electron/nuclear recoil : 170 LXe K LAr + ( ), 87 ( ) Xe2 ✦self shielding very effective Excitation - : +e- for external background (recombination) wavelength reduction * ** depends on gas Xe Xe + Xe ✦low threshold high e.g. Xe 175nm : Ar 128nm +Xe scintillation yield (~50,000 photons MeV / ) Xe * 175nm 2 175nm ✦n recoil discrimination by Triplet Singlet - : 27ns 3ns charge to light ratio and - - time constants PSD 2Xe 2Xe depend on gas e.g. Xe 3/27ns Nigel Smith, RAL Ar 10/1500ns 8 The XENON two phase TPC concept - Top PMT Array WIMPs Neutrons / nuclear recoil Gammas electron recoil 9 Signals from XENON 10 S S 1 Xe+ 2 Ionisation +Xe Electron/nuclear recoil + Xe2 Excitation +e- (recombination) Xe* Xe** + Xe S +Xe 1 Xe * 175nm 2 175nm S Triplet Singlet 27ns 3ns 2 2Xe 2Xe 10 Why Liquid Xenon for Dark Matter Detection WIMP Scattering Rates u Large A (~ 131) good for SI σ~ A2 if low Eth 18 evts/100-kg/year u 129Xe (26.4%) & 131Xe (21.2%) good for SD σ (Eth=5 keVr) u No radioactive isotopes (Kr85 can be removed) 8 evts/100-kg/year u High stopping power (Z=54, ρ=3 g/cc) (Eth=15 keVr) u Efficient and fast scintillator (~ 80% of NaI) u Good ionization yield (W=15.6 eV) u Modest quenching factor for NR (0.14 - 0.2) u Background Rejection: Charge and Light detection (> 99.5%) plus 3D localization and self-shielding u ‘Easy’ cryogenics at ~165K u Inert, not flammable, very good dielectric u Modest cost for large mass detector 11 12 The XENON Phased Program • XENON Concept: two-phase XeTPC, 3D position sensitive, self-shielded by an active LXe veto with simultaneous charge & light detection for event-by-event discrimination (>99.5%) • XENON reached σ cm sensitivity for GeV WIMP in 10: ~10-43 2 100 2007 ➡a very successful first demonstration of the approach • XENON projected sensitivity reach σ x cm for GeV WIMP by 100: ~2 10-45 2 100 2009 ➡currently under final commissioning at LNGS Physics run starts Spring Supported . 2009. by NSF DoE and foreign contributions , • XENON Upgrade projected sensitivity reach σ x cm for GeV WIMP by 100 : ~2 10-46 2 100 2012 ➡Proposed to NSF DoE and foreign contributions , • XENON T projected sensitivity reach σ cm for GeV WIMP by 1 : ~10-47 2 100 2014 ➡Under study by larger collaboration in US Europe Japan Started to test key , , . technologie The XENON Dark Matter Search Phases the past the current the future (2005 - 2007) (2007-2010) (2010-2014) Xe+ Ionisation +Xe Electron/nuclear recoil + Xe2 Excitation +e- (recombination) Xe* Xe** + Xe +Xe Xe * 175nm 2 175nm Triplet Singlet 27ns 3ns 2Xe 2Xe XENON 10 XENON XENON T Achieved σSI 100 1 (2007) =8.8 Projected σSI x cm Projected σSI cm x cm (2009) ~2 10-45 2 (2014) ~10-47 2 10-44 2 14 Liquid Detector Medium LXe behaves like most other liquids. PTR We can use this for detector design. Head 1. Odd shaped detectors LN2 Emergency 2. Transporting heat (cold) Coolng Coil 3. Efficient conversion gas - liquid But, it also might freeze. Funnel Recirculation Gas In Gas Detector Vessel Liquid Liquid Level In equilibrium state direct relation between Active pressure and temperature. Therefore, two Volume ways to control the liquid. Recirculation Temperature regulated: PTR cooling Gas Out Pressure regulated: Emergency LN2 cooling 15 XENON Gamma Neutron calibration 10 / ~ 99.5 % gamma events are rejected below the nuclear recoil mean XENON WIMP Nucleon Cross Section Upper Limits 10 - - Spin independent Spin ependent - - Phys Rev Lett Phys Rev Lett . 100, 021303 (2008) . 101, 091301 (2008) II - CDMS ZEPLIN II 10 CDMS XENON 10 XENON NO BKG SUBTRACTION ( ) x cm at Constrained Minimal 8.8 10-44 2 100 NO BKG SUBTRACTION GeV Supersymmetric Model( ) x -39 cm2 at GeV x cm at 6 10 30 4.5 10-44 2 30 GeV 17 The Energy Resolution of the XENON TPC 10 keV keV 583 Th 239 σ -228 σ E E with activated xenon / = 2.6 % / = 2.0 (% ) single scatter events ( - ) keV 511 σ E / = 2.0 % Xe m -131 keV 164 keV 727 σ E 1.6% ( / ) keV 860 S Saturated ( 2 ) σ E / = 2.4 % quite good for neutrinoless double beta decay of Xe .. - 136 Xe + Ionisation 27 +Xe Electron/nuclear recoil1x10 y, 30-100 meV + vsXe 2 Excitation 1% 3% +e - (recombination) Xe * Xe ** + Xe +Xe Xe * 175nm 2 175nm Triplet Singlet 27ns 3ns 2Xe 2Xe 19 XENON 100 A new low background TPC x less than (100 XENON in improved shield at LNGS 10) kg LXe vs kg in XE • 170 ( . 20 10); kg fiducial mass vs kg in 50 ( . 5 Xe+ XE x fiducial mass Ionisation 10). 10 low radioactivity and high QE PMTs +Xe • : Electron/nuclear recoil Hamamatsu R vs in 242 8520 ( . 89 XE + 10) Xe2 Excitation low activity cryostat inner chamber • & +e- improved shielding x lower & :100 (recombination) background Xe* Xe** + Xe +Xe Xe * 175nm 2 175nm Triplet Singlet 27ns 3ns 2Xe 2Xe 20 Status of XENON the TPC Assembly 100: 21 22 XENON Keeping it Cold New Cryogenics System Design 100: ! 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 Xe+ Ionisation +Xe Electron/nuclear recoil + Xe2 Excitation +e- (recombination) Xe* Xe**+ Xe +Xe Xe* 175nm 2 175nm Triplet Singlet 27ns 3ns 2Xe 2Xe XENON Materials Screening for low Radioactivity 100 + Xe + Xe Ionisation Ionisation +Xe Radioactivity of all Electron/nuclear recoil +Xe Xe + materials used in 2 Electron/nuclear recoil Excitation XENON measured +e - 100 Xe+ (recombination) with a dedicated 2 Xe * Xe ** + Xe Excitation HPGe counter at +Xe +e- +Xe LNGS Xe * (recombination) 175nm 2 175nm Triplet Singlet Xe* Xe**+ Xe 27ns 3ns 2Xe 2Xe +Xe Xe* 175nm 2 175nm Triplet Singlet 27ns 3ns 2Xe 2Xe 24 Background simulations mBq PMT x PMTs gives • 0.15 / 242 3000 U decays day 238 / Each U decay produces gammas and • 238 15 9 alphas M gamma year • 16 / A• alpharealisticn reactionmodelresults basedneutron yearon ( , ) 7 / Geant was constructed to 4 propagate all the gammas neutrons and / simulate the expected background rate in XENON 25 100. Expected Background and Sensitivity Reach druee evts keVee kg day = / / / e assume cross section -44 cm2 10 26 XENON Data Acqusition System 100: 27 First signals from XENON 100 • XENON is filled with kg of Xe and running in stable conditions 100 170 at LNGS • Light and charge yields improving with continuous purification of the liquid by hot getter • Currently pe keV estimated light collection is pe keV 2.7 / ; 4-5 / 28 XENON background run 100 data Simulation edge events with poor light collection will be removed by all single multiple , / radial position cut scattering events all single multiple / scattering events single scatter only with kg fiducial ~46 mass cut 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. 29 XENONXENON KrKr RemovalRemoval 100:100: Kr Beta Emax keV t y br 85 ( , = 687 , = 10.8 , = Rb 99.563%) -> 85 Kr Beta Emax keV t y br 85 ( , = 173 , = 10.8 , = 0.434%) Rb m Gamma E keV t us -> 85 ( , = 514 , = 2.43 ) -> Rb 85 XENON science goal requires Kr contamination 100 ~ ppt 50 We use cryogenic distillation to separate Kr from Xe : distilled by Spectra Gases Industry to ppb Kr 1) < 10 level verified with XENON data by delayed coincidences 100 analysis Measured Kr contamination ppb = 7+-2 distilled on site by dedicated Cryogenic Distillation 2) Tower designed to reduce Kr by factor 3 at a rate of 10 0.6 kg hr / 30 We reached reduction by Column parameters have >10. been fine tuned in first commissioning run during Sep 08. Next run of column around April 3) . With continuous recirculation the purity improves with time. Main impurities, but there are others: Purity for light is determined by water. Purity for charge is also determined by oxygen. Purification of Gas. Recirculation speed about 10 SLPM Cleaning time for XENON10: 2 months We monitor: Initially: light yield ( S1 ) Then: Charge yield vs. drift time ( S2 ) Cleaning of Detector takes time. Time – “Driver” is out gassing rate, not recirculation speed. New Photodetector for XENON : Low Radioactivity Single Photon Counting high QE - - 33 Proposed upgrade for XENON 100 (2009-2012) 34 Sensitivity Reach of the XENON Program 100 Current Best Sensitivity 2011- 2009 2012 35 XENON T Detector for pre DUSEL era before 1 - ( 2014) Multi ton XENON Detector for DUSEL beyond - ( 2014)