arXiv subjects

K. Hiraide

Publications and source records attributed to K. Hiraide.

At least 73 records · Page 4Linked to original sources

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↗

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

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

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 $4.7 \times 10^{21}$ 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 $4.3 \times 10^{21}$ years at 90% confidence level as well.

nucl-ex↗

arXiv2014

Search for bosonic superweakly interacting massive dark matter particles with the XMASS-I detector

Bosonic superweakly interacting massive particles (super-WIMPs) are a candidate for warm dark matter. With the absorption of such a boson by a xenon atom these dark matter candidates would deposit an energy equivalent to their rest mass in the detector. This is the first direct detection experiment exploring the vector super-WIMPs in the mass range between 40 and 120 keV. Using 165.9 days of data no significant excess above background was observed in the fiducial mass of 41 kg. The present limit for the vector super-WIMPs excludes the possibility that such particles constitute all of dark matter. The absence of a signal also provides the most stringent direct constraint on the coupling constant of pseudoscalar super-WIMPs to electrons. The unprecedented sensitivity was achieved exploiting the low background at a level $10^{-4}$ kg$^{-1}$keV$_{ee}^{-1}$day$^{-1}$ in the detector.

astro-ph.CO↗

arXiv2014

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

A search for inelastic scattering of Weakly Interacting Massive Particles (WIMPs) on the isotope $^{129}$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 $^{129}$Xe nuclei of 3.2 pb at the 90% confidence level.

astro-ph.CO↗

arXiv2013

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

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 5.6ton days of liquid xenon, the model-independent limit on the coupling for mass $\ll$ 1keV is $|g_{aee}|< 5.4\times 10^{-11}$ (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 250eV, respectively. In the mass range of 10-40keV, this study produced the most stringent limit, which is better than that previously derived from astrophysical arguments regarding the Sun to date.

astro-ph.CO↗

arXiv2013

Light WIMP search in XMASS

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$\cdot$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.

astro-ph.CO↗

arXiv2013

XMASS detector

The XMASS project aims to detect dark matter, pp and $^{7}$Be solar neutrinos, and neutrinoless double beta decay using ultra pure liquid xenon. The first phase of the XMASS experiment searches for dark matter. In this paper, we describe the XMASS detector in detail, including its configuration, data acquisition equipment and calibration system.

physics.ins-det↗

arXiv2012

Dual baseline search for muon antineutrino disappearance at 0.1 eV^2 < Δm^2 < 100 eV^2

The MiniBooNE and SciBooNE collaborations report the results of a joint search for short baseline disappearance of \bar{ν_μ} at Fermilab's Booster Neutrino Beamline. The MiniBooNE Cherenkov detector and the SciBooNE tracking detector observe antineutrinos from the same beam, therefore the combined analysis of their datasets serves to partially constrain some of the flux and cross section uncertainties. Uncertainties in the ν_μ background were constrained by neutrino flux and cross section measurements performed in both detectors. A likelihood ratio method was used to set a 90% confidence level upper limit on \bar{ν_μ} disappearance that dramatically improves upon prior limits in the Δm^2=0.1-100 eV^2 region.

hep-ex↗

arXiv2011

Dual baseline search for muon neutrino disappearance at 0.5 eV^2 < Δm^2 < 40 eV^2

The SciBooNE and MiniBooNE collaborations report the results of a ν_μdisappearance search in the Δm^2 region of 0.5-40 eV^2. The neutrino rate as measured by the SciBooNE tracking detectors is used to constrain the rate at the MiniBooNE Cherenkov detector in the first joint analysis of data from both collaborations. Two separate analyses of the combined data samples set 90% confidence level (CL) limits on ν_μdisappearance in the 0.5-40 eV^2 Δm^2 region, with an improvement over previous experimental constraints between 10 and 30 eV^2.

hep-ex↗

arXiv2011

Measurement of K+ production cross section by 8 GeV protons using high energy neutrino interactions in the SciBooNE detector

The SciBooNE Collaboration reports K+ production cross section and rate measurements using high energy daughter muon neutrino scattering data off the SciBar polystyrene (C8H8) target in the SciBooNE detector. The K+ mesons are produced by 8 GeV protons striking a beryllium target in Fermilab Booster Neutrino Beam line (BNB). Using observed neutrino and antineutrino events in SciBooNE, we measure d2σ/dpdΩ = (5.34 \times 0.76) mb/(GeV/c \times sr) for p + Be -> K+ + X at mean K+ energy of 3.9 GeV and angle (with respect to the proton beam direction) of 3.7 degrees, corresponding to the selected K+ sample. Compared to Monte Carlo predictions using previous higher energy K+ production measurements, this measurement, which uses the NUANCE neutrino interaction generator, is consistent with a normalization factor of 0.85\times0.12. This agreement is evidence that the extrapolation of the higher energy K+ measurements to an 8 GeV beam energy using Feynman scaling is valid. This measurement reduces the error on the K+ production cross section from 40% to 14%.

hep-ex↗

arXiv2011

Scintillation-only Based Pulse Shape Discrimination for Nuclear and Electron Recoils in Liquid Xenon

In a dedicated test setup at the Kamioka Observatory we studied pulse shape discrimination (PSD) in liquid xenon (LXe) for dark matter searches. 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 to 7.7\pm1.1(stat)\pm1.2 0.6(sys)\times10-2 at energies between 4.8 and 7.2 keVee and to 7.7\pm2.8(stat)\pm2.5 2.8(sys)\times10-3 at energies between 9.6 and 12 keVee for a scintillation light yield of 20.9 p.e./keV. Further study was done by masking some of that light to reduce this yield to 4.6 p.e./keV, the same method results in an electron event reduction of 2.4\pm0.2(stat)\pm0.3 0.2(sys)\times10-1 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.

physics.ins-det↗

arXiv2011

Measurement of inclusive charged current interactions on carbon in a few-GeV neutrino beam

The SciBooNE Collaboration reports a measurement of inclusive charged current interactions of muon neutrinos on carbon with an average energy of 0.8 GeV using the Fermilab Booster Neutrino Beam. We compare our measurement with two neutrino interaction simulations: NEUT and NUANCE. The charged current interaction rates (product of flux and cross section) are extracted by fitting the muon kinematics, with a precision of 6-15% for the energy dependent and 3% for the energy integrated analyses. We also extract CC inclusive interaction cross sections from the observed rates, with a precision of 10-30% for the energy dependent and 8% for the energy integrated analyses. This is the first measurement of the CC inclusive cross section on carbon around 1 GeV. These results can be used to convert previous SciBooNE cross section ratio measurements to absolute cross section values.

hep-ex↗

arXiv2010

Measurement of neutral current coherent neutral pion production on carbon in a few-GeV neutrino beam

The SciBooNE Collaboration reports a measurement of neutral current coherent neutral pion production on carbon by a muon neutrino beam with average energy 0.8 GeV. The separation of coherent from inclusive neutral pion production has been improved by detecting recoil protons from resonant neutral pion production. We measure the ratio of the neutral current coherent neutral pion production to total charged current cross sections to be (1.16 +/- 0.24) x 10-2. The ratio of charged current coherent pion to neutral current coherent pion production is calculated to be 0.14+0.30 -0.28, using our published charged current coherent pion measurement.

hep-ex↗

arXiv2010

Measurement of Inclusive Neutral Current Neutral Pion Production on Carbon in a Few-GeV Neutrino Beam

The SciBooNE Collaboration reports inclusive neutral current neutral pion production by a muon neutrino beam on a polystyrene target (C8H8). We obtain (7.7 \pm 0.5(stat.) \pm 0.5 (sys.)) x 10^(-2) as the ratio of the neutral current neutral pion production to total charged current cross section; the mean energy of neutrinos producing detected neutral pions is 1.1 GeV. The result agrees with the Rein-Sehgal model implemented in our neutrino interaction simulation program with nuclear effects. The spectrum shape of the neutral pion momentum and angle agree with the model. We also measure the ratio of the neutral current coherent pion production to total charged current cross section to be (0.7 \pm 0.4) x 10^(-2).

hep-ex↗