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XMASS 2012 Symposium on Particle Physics and Cosmology

Learn about XMASS experiment analyzing solar neutrinos, dark matter, and double beta decay using liquid Xenon. Discusses detector characteristics, construction, performance, and background evaluation.

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XMASS 2012 Symposium on Particle Physics and Cosmology

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  1. XMASS 2012 Shanghai Particle Physics and Cosmology Symposium Hiroshi Ogawa (ICRR, Univ. of Tokyo) Sep. 16th , 2012

  2. Solar neutrino XMASS experiment Multi purpose low-background and low-energy threshold experiment with liquid Xenon pp/7Be chain: n+e  n+e Dark matter χ+Xe  χ+Xe Double beta 136Xe  136Ba + 2e- • Liquid Xenon : • Large photon yield Low threshold Scintillation wavelength (175 nm, detected directly by PMT) • High density (~3 g/cm3) Compact detector • Large Z (=54) Self-Shielding • ~-100℃ liquid : easy to use. • Purification (distillation) • No long life radioactive isotope 2

  3. Direct Detection Principle Dark Matter （WIMP） Deposit Energy WIMPs elastically scatter off nuclei in targets, producing nuclear recoils. R0: Event rate F: Form Factor should be calculated in each nuclei Maxwellian distribution for DM velocity is assumed. v0:dispersion V :velocity onto target, VE: Earth’s motion around the Sun Spin independent case: Larger A is higher event rate Xe (A=131) is one of the best target. From the density of dark matter in the galaxy: Every liter of space: 10-100 WIMPs, moving at 1/1000 the speed of light Less than 1 WIMP/week will collide with an atom in 1kg material

  4. Characteristics of XMASS • XMASS : single phase detector • Large volume and simple structure, operation. • 1 ton scale xenon detector, 100kg for fiducial volume. • Background reduction technique : • Self shielding • Reconstruction by hit pattern of PMTs • High light yields & Large photon coverage (15 pe/keV) • Low energy threshold (< 5 keVee ~ 25 keVNR ) for fiducial volume • Lower energy threshold: 0.3 keV for whole volume • Large Scalability, simple to construct. Self shielding 10ton 1ton

  5. XMASS detector 5

  6. XMASS detector : site Elec. hut KamLAND Water tank Refrigerator Super-K CANDLES XMASS (Lab-C) 11m Lab2/EGad IPMULab1 CLIO NEWAGE 10m 72 20inch PMTs (veto) Kamioka Mine Kamioka Mine Tokyo • 72 20-inch PMTs are 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.

  7. Structure of XMASS detector 1.2m diameter • Detector • Single phase (scintillation only) liquid Xenon detector • Operated at -100oC and ~0.065MPa • 100 kg fid. mass, [835 kg inner mass (0.8 mf)] • Pentakis-dodecahedron  12 pentagonal with 5 triangle • 630 hexagonal & 12 round PMTs with 28-39% Q.E. • photocathode coverage: > 62% inner surface

  8. Detector construction 2010 1st application of WC tank for WIMP search 8 By fall, 2010

  9. Detector performance 9

  10. Data taking :commissioning run Nov.2010-June.2012 • PMT gain reduced run • Evaluate the signal from radon daughter in xenon. • Gas run • Important to identify the surface BG • BG measurement of the detector parts（attach the material at the end of the calibration source rod） • Al, GORE-TEX, Cu, Ni plate • Calibration • Source Rod (57Co, 241Am, 137Cs, 109Cd, 55Fe) • External sources: 60Co, 137Cs, 232Th, Neutron • Normal Data taking (physics runs) • Change of the physical condition of Xenon. • High/Low pressure run • Change of the refractive index of Xe • O2 runs: change of the absorption length • Boiling runs: create convection inside of the detector

  11. Detector response for a point-like source (~WIMPs) RI source with rod 122keV total photo electron ~4% rms +15V data MC reconstructed vertex 136keV data MC 59.3keV of W 57Co source @ center gives a typical response of the detector. 14.7p.e./keVee( 2.2 for S1 in XENON100) The pe dist. well as vertex dist. were reproduced by a simulation well. Signals would be <150p.e. exp shape.

  12. Measured Spectrum (Whole Volume) and background evaluation Gamma from PMTs had been assumed as mainly background sources Gamma from PMTs ~200keV Observed data ~1MeV MC: PMT g rays ~50keV • RI of PMT are measured by HPGe detector per PMT parts. • (+40% for 60Co) • Data has large excess in <200keV compared with data. • ~x100 difference in ~5keV ~x100 Energy spectrum data and PMT MC

  13. Measured Spectrum (Whole Volume) and background evaluation These background are faced to liquid xenon. X-ray and beta from RI emit to Liquid xenon directly. RI from PMT aluminum seal • Aluminum sealing used for the PMT between quarts window and metal body. It contains 238U-230Th and 210Pb-206Pb. Observed data ~1MeV ~1MeV MC: PMT g rays MC: PMT Al 238U & Pb210 Surface 210Pb Aluminum Seal ~50keV 210Pb on detector surface 222Rn daughter put btw. construction work

  14. Measured Spectrum (Whole Volume) and background evaluationBelow 5keV 14C in GORE-TEX MC: GORE-TEX Modern C: 7.5% LXe inside scintillate 0.3mm photon att. ~5keV MC: GORE-TEX Modern C: 7.5% LXe inside scintillate 0.1mm photon att. ~5keV mDM= 18 GeV sSI= 1.6x10-41cm2 mDM = 30GeV sSI = 1.4x10-41cm2 • GORE-TEX: between PMT and holder used for a light seal. It contains 0~6±3% of modern carbon. • GORE-TEX might explain the background below 5keV • But parameters ( ex. transparency of light inside of GORE-TEX) are not well known • We will remove GORE-TEX in future detector refurbishment

  15. Background estimates

  16. Low background even with the surface BG • Our BG is still quite low, even with the extra surface BG! • In principle, the surface BG can be eliminated by vertex reconstruction. Optimization of the reconstruction program is on going to minimize a possible leakage to the inner volume. • Our sensitivity for the low mass WIMP signals at low energy without reconstruction will be shown. Evens/kg/day/keV XMASS full volume E. Aprile, 2010 Princeton 16

  17. Physics analysis 17

  18. Physics analysis(sensitivity study) Light WIMPs & ALP: Low threshold BG less important Standard WIMPs: Prefer heavy mass Low BG • Whole Volume Analysis (Large BG, Large target mass of 835 kg, low energy threshold, no reconstruction) 1) 4 hit threshold analysis • Low mass region search 2) 1keVee threshold analysis • Check DAMA modulation • Axion DM (super-WIMPs) • Solar Axions • Fiducial Volume analysis 1) Standard WIMPs search (> 5 keV) • Event reconstruction/reduction

  19. Physics analysis: Low energy, full volume analysis for low mass WIMPs Light WIMPs & ALP: Low threshold BG less important Selection criteria for data: • Triggered by the inner detector only (no water tank trigger) • RMS of hit timing <100ns (rejection of after pulses of PMTs) • Cherenkov rejection • Time difference to the previous/next event >10ms The dark matter signal rapidly increase toward low energy end. The large p.e. yield enables us to see light WIMPs. Try to set absolute maxima of the cross section (predicted spectrum must not exceed the observed spectrum). The largest BG at the low energy end is the Cherekov emission from 40K in the PMT photo cathodes.

  20. Detail of the Cherenkov rejection 20 Cherenkov like Scintillation like Black: real data Black: real data Blue: DM MC Head total ratio Head total ratio 20ns 20ns (PE) (PE) Total # of hits Total # of hits 0 40 80 120 160 200 0 40 80 120 160 200 • Cherenkov events peaks around 1  scintillation ~ 0.5 • Low energy events observed in Fe55 calibration source as well as DM simulation (t=25ns) show similar distributions. • Efficiency ranges from 40% to 70% depending on the p.e. range. Basically, separation between scintillation lights and Cherenkov lights can done using timing profile. (# of hits in 20ns window) / (total # of hits) = “head total ratio” is a good parameter for the separation.

  21. p.e. distribution after each cut 21 ID only event (trigger ID == 1) dT > 10ms RMS of hit timing < 100ns Cherenkov cut 6.8 days x 835kg data The Cherenkov events are efficiently reduced by the cut. We analyze the events above > 0.3 keVee for entire volume

  22. Uncertainties 22 Scintillation efficiency as a function of energy E. Aprile et al., PRL 105, 131302 (2010) • Major uncertainty is the scintillation efficiency of nuclear recoil in liquid xenon. • Uncertainties of the trigger thre. (hard trig. 4hits), cut eff., and energy scale are also properly taken into account.

  23. Spectrum and Sensitivity 23 DAMA CoGeNT XMASS Count/day/kg/keVee WIMP cross section on nucleon (cm2) Preliminary XMASS observed energy [keVee] Spectrum shows that observed data and MC WIMPs signal with best fit per WIMPs mass. Sensitive to the allowed region of DAMA/CoGeNT. Some part of the allowed regions can be excluded. GeV

  24. Progress of annual modulation analysis • Check the DAMA modulation • QF(Na)~0.25, Leff(Xe)~0.15 • 2~6keVee(Na)  8~24 keVNR  1~4keVee(Xe) • but 1/30 sensitivity  recoil shape, A2 • c2: 10.8 for flat, 23.8 for a modulation 2013 data taking (after refurbishment) will cover the maximum and minimum flux region. 1-4 keVee(Xe)  2-6 keVee (Na) Preliminary

  25. Dark matter axion search in XMASS gaee The DAMA signal may be due to electromagnetic interaction of WIMPs to the NaI detectors by such as a non-relativistic axion dark matter. See J. Collar, arXiv: 0903.5068 XMASS can search for dark matter axion by detection through axio-electric effect. We show a preliminary result based on 6.8 days x 835kg data.

  26. Limit on the axio-electric coupling Observed spectrum Expectation for ma=3keV • We obtained a limit on the axio-electric coupling (gaee) by comparing the observed spectrum and the expectation. • The result can be further improved above 5keV by fitting spectrum. Events/keV/kg/day gaee (keVee) Preliminary DAMA allowed CoGeNT CDMSXMASS Sensitivity with spectrum fitting with background MC

  27. Solar axion search in XMASS • XMASS can also search for solar axion emitted owing to Bremsstrahlung and Compton processes in the Sun, by detection through axio-electric effect. • We obtained a limit on axio-electric coupling (gaee) Solar axion flux (Derbin et al., arXiv:1206.4142) Observed spectrum MC axion signals Abs upper limit gaee=4.5e-11 gaee=10-10

  28. Limits on gaee from XMASS (DM+solar) Original figure from Derbin et al., 1206.4142 Preliminary XMASS Limit by solar axion 4.5e-11 XMASS Limit by DM Solar limit 2.8e-11 Allowed mass < 200eV for KSVZ <2eV for DFSZ

  29. Future plan 29

  30. Plan: Refurbishment work Tuning of reconstruction/reduction is on going but for better sensitivity, removing the origins of BG must be done. To reduce the BG caused by Aluminum, we are planning to cover the part and surfaces by copper rings and plates: BG > 5keV must be reduced significantly (1/100 of current BG). Schedule: start physics run from 2013

  31. Expected sensitivity with fiducialization Spin Independent Initial target of the energy threshold was ~5keVee. Because we have factor ~3 better photoelectron yield, lower threshold = smaller mass dark matter may be looked for. XMASS 5keVee thre. 100d Expected energy spec. CDMSII XENON100 1 year exposure scp=10-44 cm2 50GeV WIMP XMASS 2keVee thre. 100d Black:signal+BG Red:BG 31

  32. XMASS1.5 (2015-) • Total mass: 5 tons • Fiducial mass: 1 ton  100kg • Backgrounds • No dirty aluminum • No GORETEX • Less surface 210Pb • New PMTs. • Expect 10-5 dru • Sensitivity sSI < 10-46 cm2 (> 5 keV) • Low threshold analysis could reach a few x 10-42 cm2 around a few GeV region. DAMA CoGeNT EDELWEISSII CDMSII XENON100

  33. Summary The XMASS 800kg detector was constructed and started commissioning late 2010. We completed commissioning data-taking and physics analyses are on-going. BG level is not as low as originally expected, but now the composition is well understood above 5keV. Some preliminary results on dark matter and axion searches are shown. More results will come later. By improving software (reconstruction/BG reduction) and hardware refurbishment, we aim at the dark matter search with the original sensitivity. And XMASS1.5 will progress. Physics run is planed from 2015.

  34. XMASS collaboration ICRR, University of Tokyo K. Abe, K. Hieda, K. Hiraide, Y. Kishimoto, K. Kobayashi, Y. Koshio, S. Moriyama, M. Nakahata, H. Ogawa, H. Sekiya, A. Shinozaki, Y. Suzuki, O. Takachio, A. Takeda, D. Umemoto, M. Yamashita, B. Yang IPMU, University of Tokyo J. Liu, K. Martens Kobe University K. Hosokawa, K. Miuchi, A. Murata, Y. Ohnishi, Y. Takeuchi Tokai University F. Kusaba, K. Nishijima Gifu University S. Tasaka Yokohama National University K. Fujii, I. Murayama, S. Nakamura Miyagi University of Education Y. Fukuda STEL, Nagoya University Y. Itow, K. Masuda, H. Takiya, H. Uchida Kobe University K. Ohtsuka, Y. Takeuchi Seoul National University S. B. Kim Sejong University N.Y. Kim, Y. D. Kim KRISS Y. H. Kim, M. K. Lee, K. B. Lee, J. S. Lee

  35. Cryogenic XMASS Xenon operating system • Xenon keeping : • Pulse tube refrigerator. • Xenon circulation : • Gas phase: < 30 L/min • Liquid phase: ~ 5 L/min • Xenon collection : • 700L liquid storage tank. • 10m3 x 2 gas storage tank. Gas circulation <30L/min emergency gas pump 100L/min gas pump Cable line filters Calibration line Water tank 10 m3 x 2 gas storage evaporator Condenser 360W filters 857kg 700L Liq. Storage liquid pump Outer vacuum • We successed the xenon filling/collection for 5 times • with keeping the amount and quality of xenon. Liquid circulation ~5L/min

  36. Internal RI in xenon Radon concentration: 222Rn : 8.2+/-0.5mBq 220Rn : <280microBq (90%C.L.) 222Rn 220Rn ※214Pb, 212Pb(daugther of radon) is source of background in low energy. These background is remained even after fiducial volume cut. 8.2mBq～2x10-4dru contribution. 164us 145ms Fitting with an expected decay curve 1st event (214Bi b) 2nd event (214Po a) 220Rn candidate 216Po candidate ~accidental 100 500 1000 Time difference (ms)

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