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K. Fushimi

Publications and source records attributed to K. Fushimi.

At least 55 records · Page 3Linked to original sources
arXiv2018

Search for dark matter in the form of hidden photons and axion-like particles in the XMASS detector

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 $g_{Ae}$ of axion-like particles in the mass range from 40 to 120 keV/$c^2$, resulting in $α' / α< 6 \times 10^{-26}$ and $g_{Ae} < 4 \times 10^{-13}$. These limits are the most stringent derived from both direct and indirect searches to date.

astro-ph.CO↗
arXiv2018

Direct dark matter search by annual modulation with 2.7 years of XMASS-I data

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$\times$10$^{-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.

astro-ph.CO↗
arXiv2018

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

We conducted an improved search for the simultaneous capture of two $K$-shell electrons on the $^{124}$Xe and $^{126}$Xe nuclei with emission of two neutrinos using 800.0 days of data from the XMASS-I detector. A novel method to discriminate $γ$-ray/$X$-ray or double electron capture signals from $β$-ray background using scintillation time profiles was developed for this search. No significant signal was found when fitting the observed energy spectra with the expected signal and background. Therefore, we set the most stringent lower limits on the half-lives at $2.1 \times 10^{22}$ and $1.9 \times 10^{22}$ years for $^{124}$Xe and $^{126}$Xe, respectively, with 90% confidence level. These limits improve upon previously reported values by a factor of 4.5.

nucl-ex↗
arXiv2018

Identification of $^{210}$Pb and $^{210}$Po in the bulk of copper samples with a low-background alpha particle counter

We established a method to assay $^{210}$Pb and $^{210}$Po contaminations in the bulk of copper samples using a low-background alpha particle counter. The achieved sensitivity for the $^{210}$Pb and $^{210}$Po contaminations reaches a few mBq/kg. Due to this high sensitivity, the $^{210}$Pb and $^{210}$Po contaminations in oxygen free copper bulk were identified and measured for the first time. The $^{210}$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 $^{210}$Pb in oxygen free copper was understood to be a small residual of an electrolysis process. This method to measure bulk contaminations of $^{210}$Pb and $^{210}$Po could be applied to other materials.

physics.ins-det↗
arXiv2017

Search for solar Kaluza-Klein axion by annual modulation with the XMASS-I detector

In theories with the large extra dimensions beyond the standard 4-dimensional spacetime, axions could propagate in such extra dimensions, and acquire Kaluza-Klein (KK) excitations. These KK axions are produced in the Sun and could solve unexplained heating of the solar corona. While most of the solar KK axions escape from the solar system, a small fraction is gravitationally trapped in orbits around the Sun. They would decay into two photons inside a terrestrial detector. The event rate is expected to modulate annually depending on the distance from the Sun. We have searched for the annual modulation signature using $832\times 359$ kg$\cdot$days of XMASS-I data. No significant event rate modulation is found, and hence we set the first experimental constraint on the KK axion-photon coupling of $4.8 \times 10^{-12}\, \mathrm{GeV}^{-1}$ at 90% confidence level for a KK axion number density of $\bar{n}_\mathrm{a} = 4.07 \times 10^{13}\, \mathrm{m}^{-3}$, the total number of extra dimensions $n = 2$, and the number of extra dimensions $δ= 2$ that axions can propagate in.

hep-ex↗
arXiv2017

Search for cosmic dark matter by means of ultra high purity NaI(Tl) scintillator

The dark matter search project by means of ultra high purity NaI(Tl) scintillator is now underdevelopment. An array of large volume NaI(Tl) detectors whose volume is 12.7 cm$ϕ\times$12.7 cm is applied to search for dark matter signal. To remove radioactive impurities in NaI(Tl) crystal is one of the most important task to find small number of dark matter signals. We have developed high purity NaI(Tl) crystal which contains small amounts of radioactive impurities, $<4$ ppb of $^{nat}$K, 0.3 ppt of Th chain, 58 $μ$Bq/kg of $^{226}$Ra and 30 $μ$Bq/kg of $^{210}$Pb. Future prospects to search for dark matter by means of a large volume and high purity NaI(Tl) scintillator is discussed.

physics.ins-det↗
arXiv2016

Search for electron antineutrinos associated with gravitational wave events GW150914 and GW151226 using KamLAND

We present a search for low energy antineutrino events coincident with the gravitational wave events GW150914 and GW151226, and the candidate event LVT151012 using KamLAND, a kiloton-scale antineutrino detector. We find no inverse beta-decay neutrino events within $\pm 500$ seconds of either gravitational wave signal. This non-detection is used to constrain the electron antineutrino fluence and the luminosity of the astrophysical sources.

astro-ph.HE↗
arXiv2016

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

We report the measurement of the emission time profile of scintillation from gamma-ray induced events in the XMASS-I 832 kg 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, $^{55}$Fe, $^{241}$Am, and $^{57}$Co were used to obtain the decay time constant. Assuming two decay components, $τ_1$ and $τ_2$, the decay time constant $τ_2$ increased from 27.9 ns to 37.0 ns as the gamma-ray energy increased from 5.9 keV to 122 keV. The accuracy of the measurement was better than 1.5 ns at all energy levels. A fast decay component with $τ_1 \sim 2$ ns was necessary to reproduce data. Energy dependencies of $τ_2$ 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.

physics.ins-det↗
arXiv2016

Direct dark matter search by annual modulation in XMASS-I

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$\times$10$^{-41}$cm$^2$ at 8 GeV/c$^2$ was obtained and we exclude almost all the DAMA/LIBRA allowed region in the 6 to 16 GeV/c$^2$ range at $\sim$10$^{-40}$cm$^2$. The result of a simple modulation analysis, without assuming any specific dark matter model but including electron/$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.

astro-ph.CO↗
arXiv2016

KamLAND Sensitivity to Neutrinos from Pre-Supernova Stars

In the late stages of nuclear burning for massive stars ($M>8~M_{\sun}$), the production of neutrino-antineutrino pairs through various processes becomes the dominant stellar cooling mechanism. As the star evolves, the energy of these neutrinos increases and in the days preceding the supernova a significant fraction of emitted electron anti-neutrinos exceeds the energy threshold for inverse beta decay on free hydrogen. This is the golden channel for liquid scintillator detectors because the coincidence signature allows for significant reductions in background signals. We find that the kiloton-scale liquid scintillator detector KamLAND can detect these pre-supernova neutrinos from a star with a mass of $25~M_{\sun}$ at a distance less than 690~pc with 3$σ$ significance before the supernova. This limit is dependent on the neutrino mass ordering and background levels. KamLAND takes data continuously and can provide a supernova alert to the community.

astro-ph.HE↗
arXiv2015

Dark matter search project PICO-LON

The PICO-LON project aims at search for cold dark matter by means of highly radio-pure and large volume NaI(Tl) scintillator. The NaI powder was purifed by chemical processing to remove lead isotopes and selecting a high purity graphite crucible. The concentrations of radioactive impurities of $^{226}$Ra and $^{228}$Th were effectively reduced to 58$\pm$4 $μ$Bq/kg and 1.5$\pm$1.9 $μ$Bq/kg, respectively. It should be remarked that the concentration of $^{210}$Pb, which is crucial for the sensitivity to dark matter, was reduced to 24$\pm$2 $μ$Bq/kg. The total background rate at 10 keVee was as low as 8 keV$^{-1}$kg$^{-1}$day$^{-1}$, which was sufficiently low to search for dark matter. Further purification of NaI(Tl) ingot and future prospect of PICO-LON project is discussed.

astro-ph.IM↗
arXiv2015

Search for double-beta decay of 136Xe to excited states of 136Ba with the KamLAND-Zen experiment

A search for double-beta decays of 136Xe to excited states of 136Ba has been performed with the first phase data set of the KamLAND-Zen experiment. The 0+1, 2+1 and 2+2 transitions of 0ν\{beta}\{beta} decay were evaluated in an exposure of 89.5kg-yr of 136Xe, while the same transitions of 2ν\{beta}\{beta} decay were evaluated in an exposure of 61.8kg-yr. No excess over background was found for all decay modes. The lower half-life limits of the 2+1 state transitions of 0ν\{beta}\{beta} and 2ν\{beta}\{beta} decay were improved to T(0ν, 0+ \rightarrow 2+) > 2.6\times10^25 yr and T(2ν, 0+ \rightarrow 2+) > 4.6\times10^23 yr (90% C.L.), respectively. We report on the first experimental lower half-life limits for the transitions to the 0+1 state of 136Xe for 0ν\{beta}\{beta} and 2ν\{beta}\{beta} decay. They are T (0ν, 0+ \rightarrow 0+) > 2.4\times10^25 yr and T(2ν, 0+ \rightarrow 0+) > 8.3\times10^23 yr (90% C.L.). The transitions to the 2+2 states are also evaluated for the first time to be T(0ν, 0+ \rightarrow 2+) > 2.6\times10^25 yr and T(2ν, 0+ \rightarrow 2+) > 9.0\times10^23 yr (90% C.L.). These results are compared to recent theoretical predictions.

hep-ex↗
arXiv2015

Study of electron anti-neutrinos associated with gamma-ray bursts using KamLAND

We search for electron anti-neutrinos ($\overlineν_e$) from long and short-duration gamma-ray bursts~(GRBs) using data taken by the KamLAND detector from August 2002 to June 2013. No statistically significant excess over the background level is found. We place the tightest upper limits on $\overlineν_e$ fluence from GRBs below 7 MeV and place first constraints on the relation between $\overlineν_e$ luminosity and effective temperature.

astro-ph.HE↗
arXiv2014

KamLAND-PICO project to search for cosmic dark matter

KamLAND-PICO project aims to search for WIMPs dark matter by means of NaI(Tl) scintillator. To investigate the WIMPs candidate whose cross section is as small as $10^{-9}$ pb, a pure NaI(Tl) crystal was developed by chemical processing and taking care of surroundings. The concentration of U and Th chain was reduced to $5.4\pm0.9$ ppt and $3.3\pm2.2$ ppt, respectively. It should be remarked that the concentration of $^{210}$Pb which was difficult to reduce reached to the high purity as $58\pm26$ $μ$Bq/kg.

astro-ph.IM↗
arXiv2012

Measurement of airborne radioactivity from the Fukushima reactor accident in Tokushima, Japan

The airborne radioactive isotopes from the Fukushima Daiichi nuclear plan t was measured in Tokushima, western Japan. The continuous monitoring has been carried out in Tokushima. From March 23, 2011 the fission product $^{131}$I was observed. The radioisotopes $^{134}$Cs and $^{137}$Cs were also observed in the beginning of April. However the densities were extremely smaller than the Japanese regulation of radioisotopes.

nucl-ex↗
arXiv2006

Multi-layer scintillation detector for the MOON double beta decay experiment: Scintillation photon responses studied by a prototype detector MOON-1

An ensemble of multi-layer scintillators is discussed as an option of the high-sensitivity detector Mo Observatory Of Neutrinos (MOON) for spectroscopic measurements of neutrino-less double beta decays. A prototype detector MOON-1, which consists of 6 layer plastic-scintillator plates, was built to study the sensitivity of the MOON-type detector. The scintillation photon collection and the energy resolution, which are key elements for the high-sensitivity experiments, are found to be 1835+/-30 photo-electrons for 976 keV electrons and sigma = 2.9+/-0.1% (dE/E = 6.8+/-0.3 % in FWHM) at the Qbb ~ 3 MeV region, respectively. The multi-layer plastic-scintillator structure with good energy resolution as well as good background suppression of beta-gamma rays is crucial for the MOON-type detector to achieve the inverted hierarchy neutrino mass sensitivity.

nucl-ex↗