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Status of XMASS experiment

Status of XMASS experiment. Hiroyoshi Uchida STE CR lab QFPU Final International Forum at Gifu miyako hotel March.8 th , 2013. Outline. Kamioka mine Introduction of XMASS Detector Background level Result of low mass WIMPs search S ummary. Kamioka mine. Map of Inside mine.

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Status of XMASS experiment

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  1. Status of XMASS experiment Hiroyoshi Uchida STE CR lab QFPU Final International Forum at Gifu miyako hotel March.8th , 2013

  2. Outline • Kamioka mine • Introduction of XMASS • Detector • Background level • Result of low mass WIMPs search • Summary

  3. Kamioka mine Map of Inside mine KamLAND Super-K CANDLES Kamioka Mine XMASS To: Atotsu mine entrance Lab2/EGad Nagoya CLIO NEWAGE

  4. XMASS experiment • What is XMASS? • Multi purpose low-background and low-energy threshold experiment with liquid Xenon. And XMASS see the Xe scintillation by nuclear recoil. • Xenon detector for Weakly Interacting MASSive Particles (DM search) • Xenon MASSive detector for solar neutrino (pp/7Be) • Xenon neutrino MASS detector (bb decay) Dark Matter Solar neutrino Double beta decay

  5. Phase of XMASS XMASS-II Multi-purpose Multi-purpose experiment using liquid xenon (-100℃) XMASS-I Final goal: 10ton fiducial volume (total 25ton) Direct detection of Dark Matter c+Xe  c+Xe pp-7Be-solar neutrino n+e n+e Double beta decay 136Xe  136Ba + 2e- • Phase I: 100kg fiducial • volume (Total 835kg) • Direct detection of Dark Matter • c+Xe c+Xe

  6. Physics of Dark matter in XMASS • low mass WIMPs (low energy threshold) • 0.3keV thre. And high light yield 14.7 p.e./keV • Heavy mass WIMPs (low background) Rate E. Aprile et al., PRL 109, 181301 (2012) E 10-39 • Phase I • Sensitivity • sSI ~ a few x 10-45 cm2 • BG 10-4 /day/kg/keV • Final goal (XMASS-II) • sSI ~ 10-47 cm2 Low background Low threshold Rate Cross section(cm2) E 10-45 10GeV 100GeV

  7. XAMSS detector • 20-inch PMT of 72 tubes will be installed to veto cosmic-ray muon (<10-6 for thr-mu, 10-4 for stop-mu). • Water is active shield for muon induced neutron and also passive shield for gamma-ray and neutron from rock/wall. • IVC and OVC are made of OFHC (Oxygen-free high thermal conductivity) copper 10.5m OVC 10m 1113mm IVC

  8. XAMSS detector 231.5mm LXe Hexagonal PMT Hamamatsu R10789 310.3mm • 60 triangles • Total: 642PMTs • Photo coverage: 62% • Diameter: ~800mm pentakisdodecahedron XMASS detector, K. Abe et al, arXiv:1301.2815 PMT holder

  9. Background level

  10. Origin of unexpected BG • Found aluminum seal parts contain 238U and 210Pb. • Simulation reproduces >5keV: reduction possible • <5keV not yet convinced. • ~100 times larger than exp. Aluminum ~5keV Real data 5.7d Simulations PMT g PMT Al GORE-TEX ~1MeV Low energy

  11. Background level compared with other experiments • Our BG is still quite low, even with the extra surface BG. • Lower than CRESST, comparable to CoGeNT, DAMA, CDMS and XENON10 before particle ID. E. Aprile, 2010 Princeton • Our sensitivity for the low mass WIMP signals at low energy without reconstruction will be shown. Evens/kg/day/keV XMASS full volume

  12. Our experiment result

  13. Low mass WIMPs search E. Aprile et al., PRL 109, 181301 (2012) • One of the interesting parameter space to be studied. • DAMA and CoGeNT saw signal/modulation • Energy deposition is smaller for them. Rate E Cross section Low threshold 10GeV • Our low-energy threshold(0.3keV  0.5keV for CoGeNT, 2keV for DAMA) is suitable for the study since the low mass WIMPs can give smaller energy.

  14. Exclusion by low mass WIMP search • 0.3 keV threshold enables us to search for low mass WIMPs. CoGeNT DAMA XMASS 6.7 days data 18GeV 12GeV 7GeV Some part of allowed region of DAMA/CoGeNT can be excluded.

  15. Summary • Phase I • Construction/operation of the largest liquid-xenon detector (835kg)is successful. Energy threshold is low (0.3keVee). • Low mass WIMPs was searched with 6.7 days data. • Light WIMP search in XMASS, K. Abe et al, accepted in Phys. Lett. B (2013), (arXiv:1211.5404) • Phase II • Larger detectors with higher sensitivity is projected. • Refurbishment (now on going) • Expected significant improvements of BG by hardware/software improvements at this summer.

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