arXiv subjects

Y. Inoue

Publications and source records attributed to Y. Inoue.

87 records · Page 5Linked to original sources

arXiv2007

A new method of alpha ray measurement using a Quadrupole Mass Spectrometer

We propose a new method of alpha($α$)-ray measurement that detects helium atoms with a Quadrupole Mass Spectrometer(QMS). A demonstration is undertaken with a plastic-covered $^{241}$Am $α$-emitting source to detect $α$-rays stopped in the capsule. We successfully detect helium atoms that diffuse out of the capsule by accumulating them for one to 20 hours in a closed chamber. The detected amount is found to be proportional to the accumulation time. Our method is applicable to probe $α$-emitting radioactivity in bulk material.

nucl-ex↗

arXiv2005

Dark matter search experiment with CaF2(Eu) scintillator at Kamioka Observatory

We report recent results of a WIMP dark matter search experiment using 310g of CaF2(Eu) scintillator at Kamioka Observatory. We chose a highly radio-pure crystal, PMTs and radiation shields, so that the background rate decreased considerably. We derived limits on the spin dependent WIMP-proton and WIMP-neutron coupling coefficients, a_p and a_n. The limits excluded a part of the parameter space allowed by the annual modulation observation of the DAMA NaI experiment.

astro-ph↗

arXiv2005

Measurement of the thickness of an insensitive surface layer of a PIN photodiode

We measured the thickness of an insensitive surface layer of a PIN photodiode, Hamamatsu S3590-06, used in the Tokyo Axion Helioscope. We made alpha-particles impinge on the PIN photodiode in various incidence angles and measured the pulse height to estimate the thickness of the insensitive surface layer. This measurement showed its thickness was $0.31 \pm 0.02 μm$ on the assumption that the insensitive layer consisted of Si. We calculated the peak detection efficiency for low energy x-rays in consideration of the insensitive layer and escape of x-rays and Auger electrons. This result showed the efficiency for 4-10keV x-rays was more than 95%.

physics.ins-det↗

arXiv2005

Exact diagonalization study of optical conductivity in two-dimensional Hubbard model

The optical conductivity σ(ω) in the two-dimensional Hubbard model is examined by applying the exact diagonalization technique to small square clusters with periodic boundary conditions up to \sqrt{20} X \sqrt{20} sites. Spectral-weight distributions at half filling and their doping dependence in the 20-site cluster are found to be similar to those in a \sqrt{18} X \sqrt{18} cluster, but different from 4 X 4 results. The results for the 20-site cluster enable us to perform a systematic study of the doping dependence of the spectral-weight transfer from the region of the Mott-gap excitation to lower-energy regions. We discuss the dependence of the Drude weight and the effective carrier number on the electron density at a large on-site Coulomb interaction.

cond-mat.str-el↗

arXiv2004

Dark Matter Search with Direction Sensitive Scintillators

We have carried out the dark matter search with a 116g direction-sensitive stilbene crystal in Kamioka Observatory. With the crystal fixed to the earth, we searched the modulation of thelight output. No modulation signal was found due to the small size of the detector crystal and the higher background rate yet to be eliminated. However, it demonstrated the effectiveness of the method of direction sensitive search for the dark matter with an implementation of the anisotropic organic scintillation crystal.

astro-ph↗

arXiv2004

Dark Matter Search with Direction Sensitive Scintillator

A direction sensitive dark matter detector using organic crystals is being developed. It exploits the anisotropic scintillation efficiency of organic crystals with respect to the direction of nuclear recoils relative to crystallographic axes. A variation of about 7% was observed in the scintillation efficiency of carbon recoils in a stilbene crystal for recoil energies of 30 keV to 1 MeV. We have performed a pilot experiment at Kamioka to prove the feasibility of this method.

astro-ph↗

arXiv2003

Limits on the WIMP-Nucleon Coupling Coefficients from Dark Matter Search Experiment with NaF Bolometer

We have performed the underground dark matter search experiment with a sodium fl uoride (NaF) bolometer array from 2002 through 2003 at Kamioka Observatory (2700 m.w.e.). The bolometer array consists of eight NaF absorbers with a total mass of 176 g, and sensitive NTD germanium thermistors glued to each of them. This experiment aims for the direct detection of weakly interacting massive part icles (WIMPs) via spin-dependent interaction. With an exposure of 3.38 kg days, we derived the limits on the WIMP-n ucleon coupling coefficients, a_p and a_n. These limits confirmed and tightened those derived from our previous results wit h the lithium fluoride (LiF) bolometer. Our results excluded the parameter space complementary to the results obtained b y NaI detectors of UKDMC experiment.

astro-ph↗

arXiv2003

Measurements of anisotropic scintillation efficiency for carbon recoils in a stilbene crystal for dark matter detection

It is known that scintillation efficiency of organic single crystals depends on the direction of nuclear recoils relative to crystallographic axes. This property could be applied to the directional WIMP dark matter detector. The scintillation efficiency of carbon recoils in a stilbene crystal was measured for recoil energies of 30 keV to 1 MeV using neutrons from $^7$Li(p,n)$^7$Be and $^{252}$Cf. Anisotropic response was confirmed in low energy regions. The variation of the scintillation efficiency was about 7 %, that could detect the possible dark matter signal.

astro-ph↗

arXiv2003

First results from dark matter search experiment with LiF bolometer at Kamioka Underground Laboratory

Tokyo group has performed first underground dark matter search experiment in 2001 through 2002 at Kamioka Observatory(2700m.w.e). The detector is eight LiF bolometers with total mass 168g aiming for the direct detection of WIMPs via spin-dependent interaction. With a total exposure of 4.1 kg days, we derived the limits in the a_p-a_n (WIMP-nucleon couplings) plane and excluded a large part of the parameter space allowed by the UKDMC experiment.

astro-ph↗

arXiv2002

Directional scintillation detector for the detection of the wind of WIMPs

The quenching factor of the proton recoil in the stilbene scintillator was measured with a 252Cf neutron source and was found to be 0.1 - 0.17 in the recoil energy range between 300 keV and 3 MeV. It was found to depend on the direction of the recoil proton. The directional anisotropy of the quenching factor could be used to detect the wind of the WIMPs caused by the motion of the earth around the galactic center.

astro-ph↗

arXiv2002

Search for sub-electronvolt solar axions using coherent conversion of axions into photons in magnetic field and gas helium

A search for solar axions has been performed using an axion helioscope which is equipped with a 2.3m-long 4T superconducting magnet, PIN-photodiode X-ray detectors, and a telescope mount mechanism to track the sun. In addition, a gas container to hold dispersion-matching gas has been developed and a mass region up to m_a=0.27eV was newly explored. From the absence of any evidence, analysis sets a limit on axion-photon coupling constant to be $g_{aγγ}<6.8-10.9\times10^{-10}GeV^{-1}$ for the axion mass of 0.05<m_a<0.27eV at 95% confidence level, which is more stringent than the limit inferred from the solar-age consideration. This result gives currently the most stringent observational limit on the existence of solar axions in this mass region.

astro-ph↗

arXiv2001

An x-ray detector using PIN photodiodes for the axion helioscope

An x-ray detector for a solar axion search was developed. The detector is operated at 60K in a cryostat of a superconducting magnet. Special care was paid to microphonic noise immunity and mechanical structure against thermal contraction. The detector consists of an array of PIN photodiodes and tailor made preamplifiers. The size of each PIN photodiode is $11\times 11\times 0.5\ {\rm mm^3}$ and 16 pieces are used for the detector. The detector consists of two parts, the front-end part being operated at a temperature of 60K and the main part in room temperature. Under these circumstances, the detector achieved 1.0 keV resolution in FWHM, 2.5 keV threshold and 6\times 10^{-5} counts sec^{-1} keV^{-1} cm^{-2} background level.

astro-ph↗

arXiv2000

Recent results from the Tokyo axion helioscope experiment

We have searched for axions which could have been produced in the solar core using an axion helioscope with a 2.3m-long 4T superconducting magnet. Axion mass region up to m_a=0.26eV was newly explored by introducing dispersion-matching gas. Preliminary analysis sets a limit on axion-photon coupling constant to be less than (6.4--9.6)e-10 GeV^{-1} (95%CL) for this mass region from the absence of the axion signal. This is more stringent than the limit inferred from the solar age consideration and also more stringent than the recent helioseismological bound.

astro-ph↗

arXiv2000

Measurement of the cross-section and forward-backward charge asymmetry for the b and c-quark in e+e- annihilation with inclusive muons at sqrt(s) = 58 GeV

We have studied inclusive muon events using all the data collected by the TOPAZ detector at sqrt(s)=58 GeV with an integrated luminosity of 273pb-1. From 1328 inclusive muon events, we measured the ratio R_qq of the cross section for qq-bar production to the total hadronic cross section and forward-backward asymmetry A^q_FB for b and c quarks. The obtained results are R_bb = 0.13+-0.02(stat)+-0.01(syst), R_cc = 0.36+-0.05(stat)+-0.05(syst), A^b_FB = -0.20+-0.16(stat)+-0.01(syst) and A^c_FB = -0.17+-0.14(stat)+-0.02(syst), in fair agreement with a prediction of the standard model.

hep-ex↗

arXiv1999

First Results from Dark Matter Search Experiment in the Nokogiriyama Underground Cell

An experiment to search for hypothetical particle dark matter using cryogenic thermal detector, or bolometer is ongoing. The bolometer consists of eight pieces of 21 g LiF absorbers and sensitive NTD germanium thermistors attached to them and is installed in the Nokogiriyama underground cell which is a shallow depth site ($\sim 15$ m w.e.). We report on the results from the first running for about ten days using this arrayed bolometer system together with appropriate shieldings and muon veto counters. From the obtained energy spectra the exclusion limits for the cross section of the elastic neutralino-proton scattering are derived under commonly accepted astrophysical assumptions. The sensitivity for the light neutralino with a mass below 5 GeV is improved by this work.

hep-ex↗