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Direct dark matter search by annual modulation with 2.7 years of XMASS-I data
Abe, K.,Hiraide, K.,Ichimura, K.,Kishimoto, Y.,Kobayashi, K.,Kobayashi, M.,Moriyama, S.,Nakahata, M.,Norita, T.,Ogawa, H.,Sato, K.,Sekiya, H.,Takachio, O.,Takeda, A.,Tasaka, S.,Yamashita, M.,Yang, B. American Physical Society 2018 Physical Review D Vol.97 No.10
<P>An annual modulation signal due to the Earth orbiting around the Sun would be one of the strongest indications of the direct detection of dark matter. In 2016, we reported a search for dark matter by looking for this annual modulation with our single-phase liquid xenon XMASS-I detector. That analysis resulted in a slightly negative modulation amplitude at low energy. In this work, we included more than one year of additional data, which more than doubles the exposure to 800 live days with the same 832 kg target mass. When we assume weakly interacting massive particle (WIMP) dark matter elastically scattering on the xenon target, the exclusion upper limit for the WIMP-nucleon cross section was improved by a factor of 2 to 1.9 x 10(-41) cm(2) at 8 GeV/c(2) at 90% confidence level with our newly implemented data selection through a likelihood method. For the model-independent case, without assuming any specific dark matter model, we obtained more consistency with the null hypothesis than before with a p-value of 0.11 in the 1-20 keV energy region. This search probed this region with an exposure that was larger than that of DAMA/LIBRA. We also did not find any significant amplitude in the data for periodicity with periods between 50 and 600 days in the energy region between 1 to 6 keV.</P>
Search for dark matter in the form of hidden photons and axion-like particles in the XMASS detector
Abe, K.,Hiraide, K.,Ichimura, K.,Kishimoto, Y.,Kobayashi, K.,Kobayashi, M.,Moriyama, S.,Nakahata, M.,Ogawa, H.,Sato, K.,Sekiya, H.,Suzuki, T.,Takachio, O.,Takeda, A.,Tasaka, S.,Yamashita, M.,Yang, B.S Elsevier 2018 Physics letters: B Vol.787 No.-
<P><B>Abstract</B></P> <P>Hidden photons and axion-like particles are candidates for cold dark matter if they were produced non-thermally in the early universe. We conducted a search for both of these bosons using 800 live-days of data from the XMASS detector with 327 kg of liquid xenon in the fiducial volume. No significant signal was observed, and thus we set constraints on the <SUP> α ′ </SUP> / α parameter related to kinetic mixing of hidden photons and the coupling constant <SUB> g A e </SUB> of axion-like particles in the mass range from 40 to 120 keV/ <SUP> c 2 </SUP> , resulting in <SUP> α ′ </SUP> / α < 6 × <SUP> 10 − 26 </SUP> and <SUB> g A e </SUB> < 4 × <SUP> 10 − 13 </SUP> . These limits are the most stringent over this mass range derived from both direct and indirect searches to date.</P>
XMASS Collaboration,Takiya, H.,Abe, K.,Hiraide, K.,Ichimura, K.,Kishimoto, Y.,Kobayashi, K.,Kobayashi, M.,Moriyama, S.,Nakahata, M.,Norita, T.,Ogawa, H.,Sekiya, H.,Takachio, O.,Takeda, A.,Tasaka, S.,Y North-Holland 2016 Nuclear Instruments & Methods in Physics Research. Vol.834 No.-
We report the measurement of the emission time profile of scintillation from gamma-ray induced events in the XMASS-I 832kg liquid xenon scintillation detector. Decay time constant was derived from a comparison of scintillation photon timing distributions between the observed data and simulated samples in order to take into account optical processes such as absorption and scattering in liquid xenon. Calibration data of radioactive sources, <SUP>55</SUP>Fe, <SUP>241</SUP>Am, and <SUP>57</SUP>Co were used to obtain the decay time constant. Assuming two decay components, τ<SUB>1</SUB> and τ<SUB>2</SUB>, the decay time constant τ<SUB>2</SUB> increased from 27.9ns to 37.0ns as the gamma-ray energy increased from 5.9keV to 122keV. The accuracy of the measurement was better than 1.5ns at all energy levels. A fast decay component with τ<SUB>1</SUB>~2ns was necessary to reproduce data. Energy dependencies of τ<SUB>2</SUB> and the fraction of the fast decay component were studied as a function of the kinetic energy of electrons induced by gamma-rays. The obtained data almost reproduced previously reported results and extended them to the lower energy region relevant to direct dark matter searches.
Abe, K.,Hieda, K.,Hiraide, K.,Hirano, S.,Kishimoto, Y.,Kobayashi, K.,Moriyama, S.,Nakagawa, K.,Nakahata, M.,Ogawa, H.,Oka, N.,Sekiya, H.,Shinozaki, A.,Suzuki, Y.,Takeda, A.,Takachio, O.,Ueshima, K.,Um North-Holland Pub. Co 2013 Physics letters: B Vol.719 No.1
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 kg@?day exposure of the detector and without discriminating between nuclear-recoil and electronic events, XMASS excludes part of the parameter space favored by other experiments.
Abe, K.,Hiraide, K.,Ichimura, K.,Kishimoto, Y.,Kobayashi, K.,Kobayashi, M.,Moriyama, S.,Nakahata, M.,Norita, T.,Ogawa, H.,Sato, K.,Sekiya, H.,Takachio, O.,Takeda, A.,Tasaka, S.,Yamashita, M.,Yang, B.S Elsevier 2018 Nuclear Instruments & Methods in Physics Research. Vol.884 No.-
<P><B>Abstract</B></P> <P>We established a method to assay <SUP>210</SUP>Pb and <SUP>210</SUP>Po contaminations in the bulk of copper samples using a low-background alpha particle counter. The achieved sensitivity for the <SUP>210</SUP>Pb and <SUP>210</SUP>Po contaminations reaches a few mBq/kg. Due to this high sensitivity, the <SUP>210</SUP>Pb and <SUP>210</SUP>Po contaminations in oxygen free copper bulk were identified and measured for the first time. The <SUP>210</SUP>Pb contaminations of our oxygen free copper samples were 17–40 mBq/kg. Based on our investigation of copper samples in each production step, the <SUP>210</SUP>Pb in oxygen free copper was understood to be a small residual of an electrolysis process. This method to measure bulk contaminations of <SUP>210</SUP>Pb and <SUP>210</SUP>Po could be applied to other materials.</P>