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 α′/α parameter related to kinetic mixing of hidden photons and the coupling constant gAe of axion-like particles in the mass range from 40 to 120 keV/c2, resulting in α′/α<6×10−26 and gAe<4×10−13. These limits are the most stringent over this mass range derived from both direct and indirect searches to date.
We have searched for exotic neutrino-electron interactions that could be produced by a neutrino millicharge, by a neutrino magnetic moment, or by dark photons using solar neutrinos in the XMASS-I ...liquid xenon detector. We observed no significant signals in 711 days of data. We obtain an upper limit for neutrino millicharge of 5.4×10−12e at 90% confidence level assuming all three species of neutrino have common millicharge. We also set flavor-dependent limits assuming the respective neutrino flavor is the only one carrying a millicharge, 7.3×10−12e for νe, 1.1×10−11e for νμ, and 1.1×10−11e for ντ. These limits are the most stringent yet obtained from direct measurements. We also obtain an upper limit for the neutrino magnetic moment of 1.8×10−10 Bohr magnetons. In addition, we obtain upper limits for the coupling constant of dark photons in the U(1)B−L model of 1.3×10−6 if the dark photon mass is 1×10−3 MeV/c2, and 8.8×10−5 if it is 10 MeV/c2.
The radioactive noble gas radon can be a serious background source in the underground particle physics experiments studying processes that deposit energy comparable to its decay products. Low energy ...solar neutrino measurements at Super-Kamiokande suffer from these backgrounds and therefore require precise characterization of the radon concentration in the detector’s ultra-pure water. For this purpose, we have developed a measurement system consisting of a radon extraction column, a charcoal trap, and a radon detector. In this article we discuss the design, calibration, and performance of the radon extraction column. We also describe the design of the measurement system and evaluate its performance, including its background. Using this system we measured the radon concentration in Super-Kamiokande’s water between May 2014 and October 2015. The measured radon concentration in the supply lines of the water circulation system was 1.74±0.14mBq∕m3 and in the return line was 9.06±0.58mBq∕m3. Water sampled from the center region of the detector itself had a concentration of <0.23mBq∕m3 (95% C.L.) and water sampled from the bottom region of the detector had a concentration of 2.63±0.22mBq∕m3.
A search for dark matter using an underground single-phase liquid xenon detector was conducted at the Kamioka Observatory in Japan, particularly for Weakly Interacting Massive Particles (WIMPs). We ...have used 705.9 live days of data in a fiducial volume containing 97kg of liquid xenon at the center of the detector. The event rate in the fiducial volume after the data reduction was (4.2±0.2)×10−3day−1kg−1keVee−1 at 5keVee, with a signal efficiency of 20%. All the remaining events are consistent with our background evaluation, mostly of the “mis-reconstructed events” originated from 210Pb in the copper plates lining the detector's inner surface. The obtained upper limit on a spin-independent WIMP-nucleon cross section was 2.2×10−44cm2 for a WIMP mass of 60GeV/c2 at the 90% confidence level, which was the most stringent limit among results from single-phase liquid xenon detectors.
The melt-crystallization behaviors of poly (l-lactic acid) (PLLA) in the presence of the external DC electric fields are reported. The real-time monitoring of the melt-crystallizations were provided ...with polarizing optical microscope at the isothermal crystallization temperatures Tc = 120 – 150 °C under the voltages VDC = 0–200 V. The crystal nucleation took place selectively at the edge of the anodes, and the highly oriented crystals grew in the direction perpendicular to the anode. The nucleation rate in the presence of the fields was much faster than that on the spherulite growth in the absence of the fields. The nucleation rate was also faster as the applied voltages were higher. On the other hand, the crystal growth rate was almost independent of the magnitude of the applied voltage value. The present experimental results indicated that the applications of the electric fields were helpful for accelerating the crystal nucleation rate of the PLLA.
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•Melt-crystallization of poly (l-lactic acid) in the presence of external field.•Real time monitoring of crystallization behaviors with polarizing optical microscope.•Highly oriented crystals grew in direction perpendicular to anode.•The crystal nucleation and growth rates were examined at different crystallization temperatures and applied voltages.•Field applications helped for accelerating crystal nucleation rate, but not for growth rate.
A search for dark matter (DM) with mass in the sub-GeV region (0.32–1 GeV) was conducted by looking for an annual modulation signal in XMASS, a single-phase liquid xenon detector. Inelastic nuclear ...scattering accompanied by bremsstrahlung emission was used to search down to an electron equivalent energy of 1 keV. The data used had a live time of 2.8 years (3.5 years in calendar time), resulting in a total exposure of 2.38 ton-years. No significant modulation signal was observed and 90% confidence level upper limits of 1.6×10−33 cm2 at 0.5 GeV was set for the DM-nucleon cross section. This is the first experimental result of a search for DM mediated by the bremsstrahlung effect. In addition, a search for DM with mass in the multi-GeV region (4–20 GeV) was conducted with a lower energy threshold than previous analysis of XMASS. Elastic nuclear scattering was used to search down to a nuclear recoil equivalent energy of 2.3 keV, and upper limits of 2.9 ×10−42 cm2 at 8 GeV was obtained.
A search for dark matter was conducted by looking for an annual modulation signal due to the Earth's rotation around the Sun using XMASS, a single phase liquid xenon detector. The data used for this ...analysis was 359.2 live days times 832 kg of exposure accumulated between November 2013 and March 2015. When we assume Weakly Interacting Massive Particle (WIMP) dark matter elastically scattering on the target nuclei, the exclusion upper limit of the WIMP–nucleon cross section 4.3×10−41 cm2 at 8 GeV/c2 was obtained and we exclude almost all the DAMA/LIBRA allowed region in the 6 to 16 GeV/c2 range at ∼10−40 cm2. The result of a simple modulation analysis, without assuming any specific dark matter model but including electron/γ events, showed a slight negative amplitude. The p-values obtained with two independent analyses are 0.014 and 0.068 for null hypothesis, respectively. We obtained 90% C.L. upper bounds that can be used to test various models. This is the first extensive annual modulation search probing this region with an exposure comparable to DAMA/LIBRA.
A search for the neutrinoless quadruple beta decay of 136Xe was conducted with the liquid-xenon detector XMASS-I using 327 kg ×800.0 days of the exposure. The pulse shape discrimination based on the ...scintillation decay time constant which distinguishes γ-rays including the signal and β-rays was used to enhance the search sensitivity. No significant signal excess was observed from the energy spectrum fitting with precise background evaluation, and we set a lower limit of the half life of 3.7 × 1024 years at 90% confidence level. This is the first experimental constraint of the neutrinoless quadruple beta decay of 136Xe.
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 |gaee|<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.
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