arXiv subjects

K. Ichimura

Publications and source records attributed to K. Ichimura.

54 records · Page 3Linked to original sources

arXiv2018

Development of the measurement for radium using germanium detector with molecular recognition resin

High-purity germanium (HPGe) detectors are widely used for the measurement of the low concentrated radioactivities. For the Super-Kamiokande-Gadolinium project, the concentration of radium in Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O is determined by using HPGe detectors. The amount of the sample is generally limited by the size of the sample space of a HPGe detector. This leads the limitation of the detector efficiency. A new method of chemical extraction using the molecular recognition resin was developed to minimize this problem. Using the developed method, radium could be extracted from Gd$_2$(SO$_4$)$_3{\cdot}$8H$_2$O and concentrated to smaller amount of the resin at a recovery rate of 81$\pm$4\%, which was estimated by using barium as a recovery monitor. This made it possible to set the sample closer to an HPGe crystal and reduce self screening effect, resulting in increasing the detection efficiency of an HPGe detector. The developed method is reported on this letter.

physics.ins-det↗

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↗

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↗

arXiv2015

7Be Solar Neutrino Measurement with KamLAND

We report a measurement of the neutrino-electron elastic scattering rate of 862 keV 7Be solar neutrinos based on a 165.4 kton-day exposure of KamLAND. The observed rate is 582 +/- 90 (kton-day)^-1, which corresponds to a 862 keV 7Be solar neutrino flux of (3.26 +/- 0.50) x 10^9 cm^-2s^-1, assuming a pure electron flavor flux. Comparing this flux with the standard solar model prediction and further assuming three flavor mixing, a nu_e survival probability of 0.66 +/- 0.14 is determined from the KamLAND data. Utilizing a global three flavor oscillation analysis, we obtain a total 7Be solar neutrino flux of (5.82 +/- 0.98) x 10^9 cm^-2s^-1, which is consistent with the standard solar model predictions.

hep-ex↗

arXiv2015

A compact ultra-clean system for deploying radioactive sources inside the KamLAND detector

We describe a compact, ultra-clean device used to deploy radioactive sources along the vertical axis of the KamLAND liquid-scintillator neutrino detector for purposes of calibration. The device worked by paying out and reeling in precise lengths of a hanging, small-gauge wire rope (cable); an assortment of interchangeable radioactive sources could be attached to a weight at the end of the cable. All components exposed to the radiopure liquid scintillator were made of chemically compatible UHV-cleaned materials, primarily stainless steel, in order to avoid contaminating or degrading the scintillator. To prevent radon intrusion, the apparatus was enclosed in a hermetically sealed housing inside a glove box, and both volumes were regularly flushed with purified nitrogen gas. An infrared camera attached to the side of the housing permitted real-time visual monitoring of the cable's motion, and the system was controlled via a graphical user interface.

physics.ins-det↗

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

Laboratory Studies on the Removal of Radon-Born Lead from KamLAND's Organic Liquid Scintillator

The removal of radioactivity from liquid scintillator has been studied in preparation of a low background phase of KamLAND. This paper describes the methods and techniques developed to measure and efficiently extract radon decay products from liquid scintillator. We report the radio-isotope reduction factors obtained when applying various extraction methods. During this study, distillation was identified as the most efficient method for removing radon daughters from liquid scintillator.

physics.ins-det↗

arXiv2011

CUORE crystal validation runs: results on radioactive contamination and extrapolation to CUORE background

The CUORE Crystal Validation Runs (CCVRs) have been carried out since the end of 2008 at the Gran Sasso National Laboratories, in order to test the performances and the radiopurity of the TeO$_2$ crystals produced at SICCAS (Shanghai Institute of Ceramics, Chinese Academy of Sciences) for the CUORE experiment. In this work the results of the first 5 validation runs are presented. Results have been obtained for bulk contaminations and surface contaminations from several nuclides. An extrapolation to the CUORE background has been performed.

nucl-ex↗

arXiv2011

Measurement of the 8B Solar Neutrino Flux with the KamLAND Liquid Scintillator Detector

We report a measurement of the neutrino-electron elastic scattering rate from 8B solar neutrinos based on a 123 kton-day exposure of KamLAND. The background-subtracted electron recoil rate, above a 5.5 MeV analysis threshold is 1.49+/-0.14(stat)+/-0.17(syst) events per kton-day. Interpreted as due to a pure electron flavor flux with a 8B neutrino spectrum, this corresponds to a spectrum integrated flux of 2.77+/-0.26(stat)+/-0.32(syst) x 10^6 cm^-2s^-1. The analysis threshold is driven by 208Tl present in the liquid scintillator, and the main source of systematic uncertainty is due to background from cosmogenic 11Be. The measured rate is consistent with existing measurements and with Standard Solar Model predictions which include matter enhanced neutrino oscillation.

hep-ex↗

arXiv2010

Chiral charge-density-waves

We discovered the chirality of charge density waves (CDW) in 1T-TiSe$_2$ by using scanning tunnelling microscopy (STM) and optical ellipsometry. We found that the CDW intensity becomes $I{a_1}:I{a_2}:I{a_3} = 1:0.7 \pm 0.1:0.5 \pm 0.1$, where $Ia_i$ (i =1, 2, 3) is the amplitude of the tunnelling current contributed by the CDWs. There were two states, in which the three intensity peaks of the CDW decrease \textit{clockwise} and \textit{anticlockwise} when we index each nesting vector in order of intensity in the Fourier transformation of the STM images. The chirality in CDW results in the three-fold symmetry breaking. Macroscopically, two-fold symmetry was indeed observed in optical measurement. We propose the new generalized CDW chirality $H_{CDW} \equiv {\boldmath $q_1$} \cdot ({\boldmath $q_2$}\times {\boldmath $q_3$})$, where ${\boldmath $q_i$}$ are the nesting vectors, which is independent of the symmetry of components. The nonzero $H_{CDW}$ - the triple-${\boldmath $q$}$ vectors do not exist in an identical plane in the reciprocal space - should induce a real-space chirality in CDW system.

cond-mat.other↗

arXiv2009

Parity Violation in a Single Domain of Spin-Triplet Sr2RuO4 Superconductors

We observed an unconventional parity-violating vortex in single domain Sr2RuO4 single crystals using a transport measurement. The current-voltage characteristics of submicron Sr2RuO4 shows that the induced voltage has anomalous components which are even function of the bias current. The results may suggest that the vortex itself has a helical internal structure characterized by a Hopf invariant (a topological invariant). We also discuss that the hydrodynamics of such a helical vortex causes the parity violation to retain the topological invariant.

cond-mat.supr-con↗

arXiv2000

Comparative study of mixed monolayers of a calixarene with a fatty acid and a non-amphiphilic nematic liquid crystal

Many nematic liquid crystals (NLCs) lack a polar headgroup and thus are not able to form stable monolayers at the air/water (a/w) interface. A way to obtain monomolecular films of these compounds is to incorporate them into host monolayers of amphiphilic molecules. We report a comparative investigation of mixed films of Calix[4]resorcinarene O-octacarboxymethylated (CRO) with the non-amphiphilic NLC MBBA and with the amphiphilic stearic acid (SA). The comparative study is useful for a better understanding of the characteristics of the CRO-MBBA mixed films. Surface-pressure and surface-potential measurements on the monolayers at a/w interface, as well as ellipsometric and spectroscopic measurements on transferred Langmuir-Blodgett (LB) films, confirm that MBBA is additively incorporated into CRO films.

cond-mat.soft↗