Current status of LUX Dark Matter Experiment by A. Lyashenko Yale University On behalf of LUX collaboration
LUX Large Underground Xenon experiment LUX Collaboration: Yale, CWRU, UC Santa Barbara, Brown, TAMU, UC Davis, Harvard, LLNL, LIPP Coimbra, Rochester, LBNL, Maryland, South Dakota SMT
WIMP Dark matter Assuming Ω DM = Ω χ WIMP DM WIMP: stable, non-barionic, non-relativistic, el. neutral m χ =10 GeV-few TeV scatter preferably from nuclei Local Milky Way DM density: ρ χ =0.3±0.1GeV cm -3 ~3 WIMPs in 1L Xe Low Energy Threshold is vital 0-80keV R Recoil Energy
WIMP direct detection: two phase Xe Top PMT Array Gamma Drift time Bottom PMT Array S2/S1 Gamma >>S2/S1 WIMP WIMP
Water Tank LUX Detector Titanium Cans Thermosyphon Top PMT Array Detector Stand 59cm 49cm Field Cage and Teflon Reflector Panels 350 kg LXe (100 kg fiducial) E d =2kV/cm, E extr =5kV/cm, E sc =10kV/cm 122 PMTs (QE~30% @ 175nm) Low Radioactivity Materials >1kW Cooling Power (Thermosyphons) Bottom PMT Array 2 Hamamatsu R8778 PMTs
Challenge: Backgrounds Sea level total muon flux: 55.2 m -2 sec -1 (threshold 300 MeV) Ambient radioactivity: ~100 evts/kg/sec Where is WIMP? Human gamma activity 40 K: ~4000 gammas/sec Walls (U/Th/K): - concrete 25/5.5/640 Bq/kg - rhyolite rock 100/45/900 Bq/kg Internal radioactivity WIMP Goal: few events/100kg/year!!!
Trickery: Going Deep Sanford Underground Research Facility (SURF) LUX 4850 feet (1478 m) underground Homestake Mine ~10 7 fold muon flux suppression 55.2 m -2 sec -1 10-5 m -2 sec -1
Trickery: Water Shield d = 8 m 6 m 20 Tonnes inverted steel pyramid 300 Tonnes of Water Cherenkov Muon Veto 20 Ø10 PMTs Gamma suppression: ~10-7 Neutron suppression (>10 MeV): ~10-3 Neutron suppression (<10 MeV): <10-9
Trickery: Understanding internal backgrounds X 122 PMTs: 10/2/65 mbq/pmt (U/Th/K) and 2 n/year/pmt Dominant source of background!!! Titanium cryostat: <0.4 mbq/kg U+Th (very low!) Cu: 10 ppt U / 12 ppt Th / 18 ppb K [~1% of ER BG budget] Radon: Cleanroom reduces levels to <40 Bq/m 3, Radon Cowl Kr: present in Xe at ppm level <2 ppt level with charcoal column PTFE: U/Th/K < 0.004/<0.001/0.053 mbq/kg 6 10-8 events/kevee/kg/day [~1% of ER BG budget]
Trickery: Xe self shielding PMT gammas PMTs are dominant background source 10 kg Fiducial volume 300 kg PMT neutrons We benefit a lot from scaling up Expect <0.5 nuclear/electron-recoils in 100 days
Trickery: ER/NR Discrimination WIMP region XENON10 data Electron Recoils Cut 2-3 kevee Nuclear Recoils High energies 99.5% Low energies 99.9%
External Sources LUX calibration Internal Sources 83m Kr (half-life 1.86 hours) 9.4 kev 32.1 kev S1 L. Kastens et al., Phys. Rev. C80: 045809,2009, A. Manalaysay et al., Rev. Sci. Instr. 81, 073303 (2010) alpha source S1 LY and kevee, e - lifetime Fills entire fiducial volume 133 Ba, 137 Cs, 22 Na, 208 Tl (collimated): S1 LY, ER energy bands, e - lifetime 241 Am/Be: NR band Tritium (half-life 12.3 yrs) Injected as CH 3 T Beta source, up to 18.6 kev Removed by purification system S2/S1 ER band Fills entire fiducial volume
LUX Program Timeline LUX Surface Run LUX DM Search Run LUX 0.1 2007-2009 2010-2011 NOW!!! 2012+
Sanford Lab Surface Facility
May 2011 first cooldown Held Target Temperature 180K Flexible Temperature Control
Expectations LUX 4000 kg-days (MC simulation) LUX ~2days LUX ~60days LUX ~300days WIMP events Targeting at 7 10-46 cm 2 (@ 100GeV) LUX strong emphasis on WIMP discovery
Future Plans: LZS/LZD Projects LZ = joint collaboration of LUX and ZEPLIN LZS (Sanford) =1500 kg (1200 kg fiducial) LUX infrastructure designed to accommodate LZ Liquid scintillator veto Construction 2012 2013, operation 2014-2015 σ χ = 2x10-47 cm 2 in 2 years LZD = 20 ton concept 2 m diameter x 2 m height Will be in a deeper site, possibly 8000 feet Construction 2014 2016, operation 2017 2020 σ χ = 10-48 cm 2 in 3 years LZD LUX
Summary Dark Matter puzzle convergence of astronomy and particle physics Evidences point to WIMPs waiting to be discovered LUX experiment uses proven liquid Xe technology to reach σ χ = 7x10-46 cm 2 Surface operation is in progress Dark Matter search run will start in 2012 Just when the LHC will be searching for New Physics LZS/LZD will push the sensitivity to 10-48 cm 2 by 2020 We may know what Dark Matter is within this decade!!!
Extra Slides
Xe signal generation
Why WIMPs?
NR scintillation efficiency E ee A. Manzur et al., arxiv:0909.1063v4 and references therein
Tritiated methane (CH 3 T) removal experiment Gaseous proportional tube counter Univ. of Maryland Xe proportional tube for CH 3 T counting Xe purifier CH 3 T storage bottle FE-55 x-ray calibration > 99.9% of CH 3 T removed from proportional tube in one pass through the purifier. Liquid xenon removal test @ UMD this spring.
Case Western Reserve University 15
New analytic technique to detect krypton at the part-per-trillion level arxiv:1103.2714v1 LN 2 Residual Gas Analyzer mass spectrometer GOAL: O(10) ppt 85 Kr - Leads to an event rate of O(0.1) events in the 2-10 kev ee regime after 10 4 kgdays and 99.5% rejection of e - recoils 1.5 ppt Kr open leak valve 16