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Search for Dark Matter at CJPL with PANDAX

Search for Dark Matter at CJPL with PANDAX. Kirill Pushkin for the PANDAX Collaboration, 10 th Rencontres du Vietnam, Very High Energy Phenomena in the Universe, August 3-9, 2014. Contents. Introduction Experiment Commissioning. Data taking. Prospects and summary.

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Search for Dark Matter at CJPL with PANDAX

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  1. Search for Dark Matter at CJPL with PANDAX Kirill Pushkin for the PANDAX Collaboration, 10th Rencontres du Vietnam, Very High Energy Phenomena in the Universe, August 3-9, 2014

  2. Contents • Introduction • Experiment • Commissioning. Data taking. • Prospects and summary

  3. PANDAX: Particle and Astrophysical Xenon

  4. The PANDAX Collaboration • Collaboration started in 2009 (includes ~40 people) • 7 institutions Shanghai Jiao Tong University, Shandong University, Shanghai Institute of Applied Physics, CAS, Beijing University, Yalong Hydropower Co., Ltd. http://pandax.org University of Michigan (USA) University of Maryland (USA)

  5. China JinPingUnderground Laboratory (CJPL) • μ – veto system unnecessary • compact shielding structure possible • easy access by road • future plans for CJPL II • ~2400 m overburden of rock • Deepest underground lab in operation 6720 m.w.e. ~57 muons/(year x m2) • Low radioactivity marble rock • Easy access – located in the middle of the 18 km tunnel

  6. CJPL SURF SURF

  7. Current layout of CJPL

  8. The PANDAX laboratory Ge counting station Xe detector Storage bottles with Gas Xenon

  9. The PANDAX Detector • Dual phase Xe detector • Probing WIMP-nucleon cross section • Designed for 1 T fiducial mass

  10. III stages for PANDAX Stage I Stage III Stage I: 125 kg xenon target, 400 kg total mass Stage II: 500 kg xenon target, 1.3T total mass Stage III: 1.5 ton target, 3T total mass Stage II

  11. External shielding Passive shield Rn purge with N2 gas • Reduces background from surrounding • rocks and concrete • Passive shield allows accommodating • a large, 1T, scale detector • Continuous flush with boiled-off LN2 • Levels of Rn achieved < 1 Bq/m3 (limited by the • sensitivity of the used Rn detector

  12. Cryogenics Cooling power ~180 W (-96 degrees of Celsius) LN cooling Pulse Tube Refrigerator Heat exchanger

  13. Stage I TPC Detector characteristics: • TPC radius: 30 cm • Drift length: 15.4 cm • Total Xenon mass: 400 kg • Sensitive target: Xe mass: 125 kg • Fiducial volume: Xe mass 37 kg • Top PMTs array (1”, R8520): 143 • Bottom PMTs array (3”, R11410): 37

  14. PANDAX- Stage I

  15. Background control: Detector materials counting Use materials with low radioactivity: 238U, 232Th, 40K, 60Co

  16. PANDAX Stage I Progress

  17. PMT calibration with LEDs • LED calibrations: • 2 Teflon ball diffusers on top PMT array • LED and diffusers are coupled to optical fibers and feedthroughs • Gains balanced at ~2x106

  18. Calibration data system We can insert a gamma or neutron source into the tubing to calibrate the detector 3D position reconstruction important for further background reduction

  19. Xenon purity • Electron lifetime ~262 us (drift time 20-80 us)

  20. S2 vs S1 light anticorrelation 80 keV (Xe-131) 40 keV (Xe-129)

  21. Gamma background rejection

  22. Radioactive background: Kr in Xe Radioisotope Kr-85, T1/2=10.756 years. Beta maximum energy decay 687 keV • We employ a home made distillation column to remove Kr from gaseous Xe. • We use an ultrasensitive Purity Analysis System based on RGA (MKS E-Vision 2). • The amount of Kr-84 in our Xe after the distillation is of the order of ppt which can be subsequently recalculated into the amount of Kr-85 in Xe. Kr-Xe distillation system

  23. Calibration measurements of Kr-84 in Xe gas Purity Analysis System Measured by K. Pushkin and He Min

  24. Sensitivity projection (Stage I after 100 days of taking data) Leffcutoff below 3 keV Leff no cut off below 3 keV Stay tuned for the Physics Results (17 days Dark Matter data paper will be released VERY SOON)

  25. Upgrade: Stage II • Goals: • Upgrade in preparations. Stay tuned for more exciting news • Sensitivity reach 2x10-46 cm2 at 100 GeV • with 54000 kg-day.

  26. Future plans: CJPL-II

  27. Summary • PANDAX has made a good progress in the past year. Currently, the experiment is taking data. • Stay tuned for the coming 17 days Dark Matter data paper (expected to appear VERY SOON on arXiv). • Currently, we are upgrading the detector, Stage I, to Stage II.

  28. Thank you for your attention!

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