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The XMASS 800kg Experiment

The XMASS 800kg Experiment. XMASS collaboration: Kamioka Observatory, ICRR, Univ. of Tokyo ： Y. Suzuki, M. Nakahata , S. Moriyama, M. Yamashita, Y. Kishimoto , Y. Koshio , A. Takeda, K. Abe, H. Sekiya , H. Ogawa, K. Kobayashi,

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The XMASS 800kg Experiment

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  1. The XMASS 800kg Experiment • XMASS collaboration: • Kamioka Observatory, ICRR, Univ. of Tokyo： • Y. Suzuki, M. Nakahata, S. Moriyama, M. Yamashita, Y. Kishimoto, • Y. Koshio, A. Takeda, K. Abe, H. Sekiya, H. Ogawa, K. Kobayashi, • K. Hiraide, A. Shinozaki, S. Hirano, D. Umemoto, O. Takachio, K. Hieda • IPMU, University of Tokyo： K. Martens, J.Liu • Kobe University:Y. Takeuchi, K. Otsuka, K. Hosokawa, A. Murata • Tokai University:K. Nishijima, D. Motoki, F. Kusaba • Gifu University： S. Tasaka • Yokohama National University： S. Nakamura, I. Murayama, K. Fujii • Miyagi University of Education： Y. Fukuda • STEL, Nagoya University： Y. Itow, K. Masuda, H. Uchida, Y. Nishitani, H. Takiya • Sejong University： Y.D. Kim • KRISS: Y.H. Kim, M.K. Lee, K. B. Lee, J.S. Lee Jing LIU IPMU, Univ. of Tokyo TAUP2011, Munich

  2. The XMASS Experiment Xenon MASSive detector for Solar neutrino (pp/7Be) Xenon neutrino MASS detector (double beta decay) Xenon detector for weakly interacting MASSive Particles PMT LXe inside ~100 kg LXe prototype ~800 kg LXe direct dark matter search ~26 ton LXe Multi-purpose LXe (Liquid Xenon) surrounded by PMTs (Photomultiplier Tubes) recording scintillation lights generated by nuclear or electronic recoils in LXe Jing LIU @ TAUP2011

  3. The XMASS Experiment Xenon MASSive detector for Solar neutrino (pp/7Be) Xenon neutrino MASS detector (double beta decay) Xenon detector for weakly interacting MASSive Particles PMT , n, ,…or ? LXe LXe inside PMT scintillation ~100 kg LXe prototype ~800 kg LXe direct dark matter search ~26 ton LXe Multi-purpose LXe (Liquid Xenon) surrounded by PMTs (Photomultiplier Tubes) recording scintillation lights generated by nuclear or electronic recoils in LXe Jing LIU @ TAUP2011

  4. The XMASS Experiment Xenon MASSive detector for Solar neutrino (pp/7Be) Xenon neutrino MASS detector (double beta decay) Xenon detector for weakly interacting MASSive Particles PMT LXe LXe inside PMT ~100 kg LXe prototype ~800 kg LXe direct dark matter search ~26 ton LXe Multi-purpose LXe (Liquid Xenon) surrounded by PMTs (Photomultiplier Tubes) recording scintillation lights generated by nuclear or electronic recoils in LXe Jing LIU @ TAUP2011

  5. The XMASS Experiment Xenon MASSive detector for Solar neutrino (pp/7Be) Xenon neutrino MASS detector (double beta decay) Xenon detector for weakly interacting MASSive Particles PMT LXe inside ~100 kg LXe prototype ~800 kg LXe direct dark matter search ~26 ton LXe Multi-purpose LXe (Liquid Xenon) surrounded by PMTs (Photomultiplier Tubes) recording scintillation lights generated by nuclear or electronic recoils in LXe Jing LIU @ TAUP2011

  6. The XMASS Experiment Xenon MASSive detector for Solar neutrino (pp/7Be) Xenon neutrino MASS detector (double beta decay) Xenon detector for weakly interacting MASSive Particles PMT LXe inside ~100 kg LXe prototype ~800 kg LXe direct dark matter search ~26 ton LXe Multi-purpose LXe (Liquid Xenon) surrounded by PMTs (Photomultiplier Tubes) recording scintillation lights generated by nuclear or electronic recoils in LXe Jing LIU @ TAUP2011

  7. The XMASS Experiment Xenon MASSive detector for Solar neutrino (pp/7Be) Xenon neutrino MASS detector (double beta decay) Xenon detector for weakly interacting MASSive Particles PMT LXe inside ~100 kg LXe prototype ~800 kg LXe direct dark matter search ~26 ton LXe Multi-purpose LXe (Liquid Xenon) surrounded by PMTs (Photomultiplier Tubes) recording scintillation lights generated by nuclear or electronic recoils in LXe Jing LIU @ TAUP2011

  8. Structure of XMASS 800kg detector PMT Jing LIU @ TAUP2011

  9. Structure of XMASS 800kg detector ~0.8 meter Pentakis dodecahedron PMT photo-cathodes cover ~62% inner surface ~10 PMTs in one triangle 642 PMTs in total PMT Jing LIU @ TAUP2011

  10. Reconstruct interaction point from PMT hit pattern Colored photo cathodes indicating number of p.e. (photoelectrons) recorded by PMTs Interaction point (vertex) can be reconstructed from the PMT hit pattern. Jing LIU @ TAUP2011

  11. LXe self-shielding Simulation: ginto LXe Attenuation length of  [cm] water LXe E[keV] Jing LIU @ TAUP2011

  12. Where is it? Kamioka underground observatory 1000 m rock overburden (2700 m water equiv.): Muon: 6.0x10-8 /cm-2/s/sr Neutron: 1.2x10-6/cm-2/s 360m above the sea Horizontal access: 15 minutes drive from office, too easy to get in! No excuse to avoid 24-hour shift  Jing LIU @ TAUP2011

  13. 15 meter 15 meter 20 meter New experimental hall, Aug. 2008 Jing LIU @ TAUP2011

  14. water tank, Nov. 2008 10 m x 10 m Jing LIU @ TAUP2011

  15. Frame of clean room in water tank, Mar. 2008 Jing LIU @ TAUP2011

  16. PMT mounting in clean room, Dec. 2009 Jing LIU @ TAUP2011

  17. PMT mounting finished, Feb. 2010 Jing LIU @ TAUP2011

  18. Water filling, Sep. 2010 Jing LIU @ TAUP2011

  19. Commissioning started, Nov. 2010 Jing LIU @ TAUP2011

  20. Scintillation light yield :: calibration system Z position of source is controlled by a motor on top at <1 mm accuracy Source changed here Top PMT can be pulled out 57Co, 241Am, 109Cd, 55Fe, 137Cs z y F~4mm x F~0.15mmfor 57Co Jing LIU @ TAUP2011

  21. Scintillation light yield: 15.9  1.2 p.e./keV (57Co at center) 122 keV Data MC Arbitrary unit 136 keV 59.3 keV (W) Number of photoelectrons Jing LIU @ TAUP2011

  22. Position & energy resolution (122keV g from 57Co) Reconstructed vertices for various source positions • Position resolution (RMS): • 1.4 cm @ z = 0 cm • 1.0 cm @ z = 20 cm Data Data MC Arbitrary unit z [cm] 122 keV Data MC RMS ~4% Arbitrary unit 136 keV 59.3 keV (W) Reconstructed energy [keV] y [cm] Jing LIU @ TAUP2011

  23. Background under control? • External • Comic ray: underground, muon veto • Ambient gamma & neutron: water shielding • PMT radiation: LXe self-shielding • Internal • Rn: material screening, clean room filled with Rn free air • Kr: distillation Jing LIU @ TAUP2011

  24. Ambient  and n: pure water tank, ~10 meter • Pure water tank (large enough for 26 ton LXe) • equipped with 20 inch PMTs on the wall as • active muon veto and • passive ambient  and n shielding g << g from PMT, n<<10-4/d/kg 20 inch PMTs 107 neutrons, simulation y [cm] Water tanks Xe LXe sphere water X [cm] Jing LIU @ TAUP2011

  25. PMT radiation: Ultra low background PMTs Calibration pipe LXe copper cryostat g n n g Neutron: <1.2x10-5dru @5-10 keV Jing LIU @ TAUP2011

  26. PMT & PMT holder radiation: LXe self-shielding Simulation: ginto LXe Counts [dru] Energy [keV] fiducial volume: r<20cm, 100 kg LXe Jing LIU @ TAUP2011

  27. 85Kr (Qb=687keV) : distillation • K. Abe et al. for XMASS collab., • Astropart. Phys. 31 (2009) 290 Kr can be boiled out from LXe 0.1 ppm ~1ppt (~1 ton in 10 days) Gas Kr outlet LXe intake Kr LXe outlet Jing LIU @ TAUP2011

  28. Kr concentration Xenon sample bg sample 1 Kr concentration: < 2.7 ppt (90% C.L.) bg sample 2 Measured by gas chromatography + API mass spectrometer Jing LIU @ TAUP2011

  29. 222Rn • 214Po decays with 164 ms half life. • It can be identified by time coincidence between two consecutive events: • 214Bi b decays into 214Po • 214Po a decays into 210Pb 8.20.5 mBq 1st event (214Bi b) 2nd event (214Po a) Events Events p0 * exp(-t/t) + p1, t: decay constant Tail due to saturation x103 Time difference [s] Number of photoelectrons Jing LIU @ TAUP2011

  30. 220Rn 216Po decays with 140 ms half life <0.28 mBq (90%C.L.) 1stevent 2ndevent Events Events p0 * exp(-t/t) + p1, t: decay constant x103 Number of photoelectrons Time difference [ms] Jing LIU @ TAUP2011

  31. Target sensitivity of WIMP-nucleon XS (spin independent) • Expected energy spectrum assuming • 1 year exposure • flat background (10-4 dru) • sc = 10-44 cm2 • MWIMP = 50 GeV • Leff= 0.2 CDMSII Black: signal + background Red: background (10-4dru) XENON100 XMASS 1yr Jing LIU @ TAUP2011

  32. Conclusion • The XMASS 800kg detector is a single phase LXe scintillation detector • Construction of the 800kg detector finished last winter • Commissioning runs are on going to confirm the detector performance and low background properties • Energy resolution and vertex resolution were as expected. ~1cm position resolution and ~4% energy resolution for 122 keVg. • Radon and Kr background are close to the target values. • The physics results are on the way Jing LIU @ TAUP2011

  33. Thanks! Jing LIU @ TAUP2011

  34. PMT holer made of OFHC copper

  35. 3 Steps in reconstruction - m m pe exp( ) å = Log( L ) Log( ) G (pe+1) PMT y 1.5cm z • Ln likelihood is calculated from the expected pe and observed pe. Using gamma distribution. • Treatment of saturated PMT, cumulative probability of gamma distribution. x Result grid of step1 • Step1 • Search the map grid where likelihood becomes smallest. • Step2 • By linear interpolation, calculate likelihood at finer “interpolated grid” in Cartesian coordinate. • 1.5cm interval, 5x5x5 finer grid points are evaluated.

  36. Integral spectrum Assumption 1x10^-44 cm^2 100 kg X 1 year exposure 25 keVr(5keVee) energy threshold 100kg x 1 year

  37. Jing LIU @ TAUP2011

  38. Jing LIU @ TAUP2011

  39. Jing LIU @ TAUP2011

  40. Jing LIU @ TAUP2011

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