Current status of LUX Dark Matter Experiment

Transcription

1 Current status of LUX Dark Matter Experiment by A. Lyashenko Yale University On behalf of LUX collaboration

2 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

3 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

4 WIMP direct detection: two phase Xe Top PMT Array Gamma Drift time Bottom PMT Array S2/S1 Gamma >>S2/S1 WIMP WIMP

5 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 175nm) Low Radioactivity Materials >1kW Cooling Power (Thermosyphons) Bottom PMT Array 2 Hamamatsu R8778 PMTs

6 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!!!

7 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 m -2 sec -1

8 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

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 events/kevee/kg/day [~1% of ER BG budget]

10 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

11 Trickery: ER/NR Discrimination WIMP region XENON10 data Electron Recoils Cut 2-3 kevee Nuclear Recoils High energies 99.5% Low energies 99.9%

12 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: ,2009, A. Manalaysay et al., Rev. Sci. Instr. 81, (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

13 LUX Program Timeline LUX Surface Run LUX DM Search Run LUX NOW!!! 2012+

14 Sanford Lab Surface Facility

15 May 2011 first cooldown Held Target Temperature 180K Flexible Temperature Control

16 Expectations LUX 4000 kg-days (MC simulation) LUX ~2days LUX ~60days LUX ~300days WIMP events Targeting at cm 2 (@ 100GeV) LUX strong emphasis on WIMP discovery

17 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 , operation 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 , operation σ χ = cm 2 in 3 years LZD LUX

18 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 cm 2 by 2020 We may know what Dark Matter is within this decade!!!

19 Extra Slides

20 Xe signal generation

21 Why WIMPs?

22 NR scintillation efficiency E ee A. Manzur et al., arxiv: v4 and references therein

23 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 UMD this spring.

24 Case Western Reserve University 15

25 New analytic technique to detect krypton at the part-per-trillion level arxiv: v1 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