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Status of the XMASS experiment

Status of the XMASS experiment. S. Moriyama for the XMASS collaboration Kamioka observatory, Institute for Cosmic Ray Research , Univ. of Tokyo, July 27, 2010, IDM2010. XMASS project. ● X MASS ◎ X enon MASS ive detector for Solar neutrino (pp/ 7 Be)

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Status of the XMASS experiment

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  1. Status of the XMASS experiment S. Moriyama for the XMASS collaboration Kamioka observatory, Institute for Cosmic Ray Research, Univ. of Tokyo, July 27, 2010, IDM2010

  2. XMASS project ●XMASS ◎ Xenon MASSive detector for Solar neutrino (pp/7Be) ◎ Xenon neutrino MASS detector (double beta decay) ◎ Xenon detector for Weakly Interacting MASSive Particles (DM search) • A large scale, multi-purpose, low background detector for astro-particle physics. Scalability and LowBG • As a first phase, an 800kg detector for dark matter search is under construction. 10ton FV (24ton) 2.5m Solar n, 0nbb, DM 100kg FV (800kg) 0.8m, DM Y. Suzukiet al., hep-ph/0008296

  3. Structure of the 800kg detector • Single phase liquid Xenon detector • 857kg of liquid xenon, 100kg in the fiducial volume • 630 hex +12 round PMTs with 28-39% Q.E. • photocathode > 62% inner surface • Pentakis dodecahedron • 3D event reconstruction • 5keVee threshold with 4.4pe/keVee Developed with Hamamatsu

  4. Background reduction 1: g/n from det. parts • /n from detector parts can be reduced by: • Reduction of RI contamination • PMTs: ~1/10 of prev. PMT achieved • OFHC: brought in the mine <1month after electrorefining(Mitsubishi Material Co.) • Material selection: >250 parts were measured by HPGe, ICPMS, Rn det. • Self shielding  < 10-4 /keV/d/kg g, n g into LXe sphere MC simulation Counts/day/kg/keV n contribution < 2x10-5/keV/d/kg keV

  5. Background reduction 2: g and n from rock • and n from rock (a,n) will be reduced by a • pure water tank  g << g from PMT, n<<10-4 /d/kg • - 11m high and 10m diameter, 72 PMTs (20’’). • - First example for dark matter experiments. • - Active veto for CR m, passive for g and n. • - Applicable for future extensions. • - Reduction of n by m’s in rock will be studied. g, n 107 n’s Att. vs. thickness y [cm] 2m g n Reduction of gamma rays water 2m PMT BG level  2m needed Liq. Xe >4m 0 1 2 3 (m) X [cm]

  6. Background reduction 3: internal radioactiv. • Kr (Qb=687keV) and Rn can be reduced by: • Distillation: Kr has lower boiling point. • 5 orders of magnitude reduction (0.1ppm  1ppt ) can be done with 4.7kg/hr: 10days for 1ton before filling into the detector. • K. Abe et al. for XMASS collab., Astropart. Phys. 31 (2009) 290 • Filtering: by gas and liquid. Under study. a, b, g Charcoal Filter GKr outlet LXe intake GXe <30 liter-GXe/m Kr LXe outlet Rn Kr LXe ~a few liter-LXe/m

  7. Expected sensitivity Spin Independent Case scp>2x10-45 cm2 for 50-100GeV WIMP, 90%C.L. 1yr exposure, 100kg FV, BG: 1x10-4 /keV/d/kg Scintillation efficiency: 0.2 XENON10 CDMSII Expected energy spectrum 1 year exposure scp=10-44 cm2 50GeV WIMP XMASS 1yr Black:signal+BG Red:BG

  8. Experimental hall, water shield, and gas handling syst. Calibration system Electronics hut Kamioka Observatory GXe buffer tank 10m3 x 2, <10bar water tank Distillation Tower LXe tank Clean booth at the entrance GXe compressor

  9. Detector Construction

  10. Construction of the PMT holder: Nov. 2009

  11. PMT installation: 311 for each half, 40 for boundary

  12. Cabling: 642 pairs of a coax and HV cable, each 13m length All the work is under Rn free air and clean environment.

  13. Joining two halves

  14. Filler attachment. Total 2.8ton: end of Feb. 2010

  15. Manufacturing detector vessel • A challenge: Manufacturing a large flange with soft OFHC copper. Inside: Electropolished • Due to insufficient strength of its neck part, it needed to be reinforced by adding ribs. • It took four months. On the 29th of July, it will be delivered.

  16. Electronics • Analog Timing Modules (ATM) used for Super-Kamiokande record charge and timing of PMTs. • FADCs record waveform of PMTs with 500MHz.

  17. Water purification system ~5m3/hour <2mBq-Rn/m3 Rn free air generator ~20m3/hour ~a few mBq-Rn/m3

  18. Schedule • August: Installation of the vessel and PMT holders at the center of the water tank. Cabling and connection of liquid/gas system will be done. • Sep.-Oct.: Distillation of xenon to reduce Kr (0.1ppm  1ppt). Evacuation of the detector, water filling test, and liquid xenon filling. • Oct.-: gas and liquid circulation starts. Reducing contamination in LXe. Data taking will start.

  19. Summary • The XMASS project aims to observe pp solar neutrinos, neutrinoless double beta decay, and dark matter signals. The 800kg detector is the first phase of the project. • It is expected to have low background of 1x10-4 keV-1 d-1kg-1 in the 100kg FV and sensitivity for SI down to 2x10-45cm2 with one year operation. • All the parts of the 800kg detector are ready and their assembly work will be finished by the end of August. • Data taking for WIMP search will be started in this year.

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