Y. Kishimoto

Search for solar axions in XMASS, a large liquid-xenon detector

Abstract XMASS, a low-background, large liquid-xenon detector, was used to search for solar axions that would be produced by bremsstrahlung and Compton effects in the Sun. With an exposure of 5.6 ton days of liquid xenon, the model-independent limit on the coupling for mass ≪1 keV is | g a e e | 5.4 × 10 − 11 (90% C.L.), which is a factor of two stronger than the existing experimental limit. The bounds on the axion masses for the DFSZ and KSVZ axion models are 1.9 and 250 eV, respectively. In the mass range of 10–40 keV, this study produced the most stringent limit, which is better than that previously derived from astrophysical arguments regarding the Sun to date.

Light WIMP search in XMASS

Abstract A search for light dark matter using low-threshold data from the single phase liquid xenon scintillation detector XMASS, has been conducted. Using the entire 835 kg inner volume as target, the analysis threshold can be lowered to 0.3 keVee (electron-equivalent) to search for light dark matter. With low-threshold data corresponding to a 5591.4 kgu2009day exposure of the detector and without discriminating between nuclear-recoil and electronic events, XMASS excludes part of the parameter space favored by other experiments.

Search for inelastic WIMP nucleus scattering on 129Xe in data from the XMASS-I experiment

A search for inelastic scattering of Weakly Interacting Massive Particles (WIMPs) on the isotope

Scintillation-only based pulse shape discrimination for nuclear and electron recoils in liquid xenon

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SENSITIVE GERMANIUM THERMISTORS FOR CRYOGENIC THERMAL DETECTOR OF TOKYO DARK MATTER SEARCH PROGRAMME

Xe was done in data taken with the single phase liquid xenon detector XMASS at the Kamioka Observatory. Using a restricted volume containing 41 kg of LXe at the very center of our detector we observed no significant excess of events in 165.9 days of data. Our background reduction allowed us to derive our limits without explicitly subtracting the remaining events which are compatible with background expectations and derive for e.g. a 50 GeV WIMP an upper limit for its inelastic cross section on

Search for two-neutrino double electron capture on 124 Xe with the XMASS-I detector

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Development of the bolometer for the β+β+ decay experiment

Xe nuclei of 3.2 pb at the 90% confidence level.

Performance of a lithium fluoride bolometer for Tokyo dark matter search experiment

Abstract In a dedicated test setup at the Kamioka Observatory we studied pulse shape discrimination (PSD) in liquid xenon (LXe) for dark matter searches in the absence of an externally applied electric field. PSD in LXe was based on the observation that scintillation light from electron events was emitted over a longer period of time than that of nuclear recoil events, and our method used a simple ratio of early to total scintillation light emission in a single scintillation event. Requiring an efficiency of 50% for nuclear recoil retention we reduced the electron background by a factor of 7.7 ± 1.1 ( stat ) ± 0.6 1.2 ( sys ) × 10 − 2 at energies between 4.8 and 7.2xa0keV ee and 7.7 ± 2.8 ( stat ) ± 2.8 2.5 ( sys ) × 10 − 3 at energies between 9.6 and 12xa0keV ee for a scintillation light yield of 20.9xa0photoelectrons/keV ee . Further study was done by masking some of that light to reduce this yield to 4.6xa0photoelectrons/keV ee . Under these conditions the same method results in an electron event reduction by a factor of 2.4 ± 0.2 ( stat ) ± 0.2 0.3 ( sys ) × 10 − 1 for the lower of the energy regions above. We also observe that in contrast to nuclear recoils the fluctuations in our early to total ratio for electron events are larger than expected from statistical fluctuations.

A measurement of the time profile of scintillation induced by low energy gamma-rays in liquid xenon with the XMASS-I detector

Abstract Sensitive n-type and p-type germanium thermistors were fabricated by the melt doping technique and by the neutron transmutation doping (NTD) technique, respectively, aiming at the use for cryogenic thermal detector, or bolometer of Tokyo dark matter search programme. We report on the measurements of the sensitivities of these thermistors. In particular, the p-type thermistors are sensitive enough to scale up our existing prototype LiF bolometer and realize a multiple array of the bolometers with the total absorber mass of about 1 kg.

Improved search for two-neutrino double electron capture on 124Xe and 126Xe using particle identification in XMASS-I

Abstract Double electron capture is a rare nuclear decay process in which two orbital electrons are captured simultaneously in the same nucleus. Measurement of its two-neutrino mode would provide a new reference for the calculation of nuclear matrix elements whereas observation of its neutrinoless mode would demonstrate lepton number violation. A search for two-neutrino double electron capture on 124 Xe is performed using 165.9 days of data collected with the XMASS-I liquid xenon detector. No significant excess above background was observed and we set a lower limit on the half-life as 4.7 × 10 21 years at 90% confidence level. The obtained limit has ruled out parts of some theoretical expectations. We obtain a lower limit on the 126 Xe two-neutrino double electron capture half-life of 4.3 × 10 21 years at 90% confidence level as well.