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K. Sakai

Publications and source records attributed to K. Sakai.

At least 91 records · Page 5Linked to original sources
arXiv2016

Measurements of cosmic-ray proton and helium spectra from the BESS-Polar long-duration balloon flights over Antarctica

The BESS-Polar Collaboration measured the energy spectra of cosmic-ray protons and helium during two long-duration balloon flights over Antarctica in December 2004 and December 2007, at substantially different levels of solar modulation. Proton and helium spectra probe the origin and propagation history of cosmic rays in the galaxy, and are essential to calculations of the expected spectra of cosmic-ray antiprotons, positrons, and electrons from interactions of primary cosmic-ray nuclei with the interstellar gas, and to calculations of atmospheric muons and neutrinos. We report absolute spectra at the top of the atmosphere for cosmic-ray protons in the kinetic energy range 0.2-160 GeV and helium nuclei 0.15-80 GeV/nucleon. The corresponding magnetic rigidity ranges are 0.6-160 GV for protons and 1.1-160 GV for helium. These spectra are compared to measurements from previous BESS flights and from ATIC-2, PAMELA, and AMS-02. We also report the ratio of the proton and helium fluxes from 1.1 GV to 160 GV and compare to ratios from PAMELA and AMS-02.

astro-ph.HE↗
arXiv2016

Galactic Cosmic Ray Origins and OB Associations: Evidence from SuperTIGER Observations of Elements $_{26}$Fe through $_{40}$Zr

We report abundances of elements from $_{26}$Fe to $_{40}$Zr in the cosmic radiation measured by the SuperTIGER (Trans-Iron Galactic Element Recorder) instrument during 55 days of exposure on a long-duration balloon flight over Antarctica. These observations resolve elemental abundances in this charge range with single-element resolution and good statistics. These results support a model of cosmic-ray origin in which the source material consists of a mixture of 19$^{+11}_{-6}$\% material from massive stars and $\sim$81\% normal interstellar medium (ISM) material with solar system abundances. The results also show a preferential acceleration of refractory elements (found in interstellar dust grains) by a factor of $\sim$4 over volatile elements (found in interstellar gas) ordered by atomic mass (A). Both the refractory and volatile elements show a mass-dependent enhancement with similar slopes.

astro-ph.HE↗
arXiv2016

Status Report for the 21th J-PARC PAC : Searching for a Sterile Neutrino at J-PARC MLF (J-PARC E56, JSNS2)

The JSNS2 (J-PARC E56) experiment aims to search for sterile neutrinos at the J-PARC Materials and Life Sciences Experimental Facility (MLF).After the submission of a proposal to the J-PARC PAC, stage-1 approval was granted to the JSNS2 experiment. The approval followed a series of background measurements which were performed in 2014. Subsequent for stage-1 approval, the JSNS2 collaboration has made continuous efforts to write a Technical Design Report (TDR).This TDR will include two major items as discussed in the previous status report for the 20th J-PARC PAC: (1) A realistic detector location (2) Well understood and realistic detector performance using simulation studies, primarily in consideration of fast neutron rejection. Since August we have been in discussions with MLF staff regarding an appropriate detector location. We are also in the process of setting up a Monte Carlo (MC) simulation framework in order to study detector's performance in realistic conditions. In addition, we have pursued hardware R&D work for the liquid scintillator (LS) and to improve the dynamic range of the 10" photomultiplier tubes (PMTs). The LS R&D works includes Cherenkov studies inside the LS, and a Pulse Shape Discrimination (PSD) study with a test-beam, performed at Tohoku University. We also estimate the PSD performance of a full-sized detector using a detailed MC simulation. In this status report, we describe progress on this work.

physics.ins-det↗
arXiv2015

Status Report for the 20th J-PARC PAC : A Search for Sterile Neutrino at J-PARC MLF (J-PARC E56, JSNS2)

On April 2015, the J-PARC E56 (JSNS2: J-PARC Sterile Neutrino Search using neutrinos from J-PARC Spallation Neutron Source) experiment officially obtained stage-1 approval from J-PARC. We have since started to perform liquid scintillator R&D for improving energy resolution and fast neutron rejection. Also, we are studying Avalanche Photo-Diodes (SiPM) inside the liquid scintillator. In addition to the R&D work, a background measurement for the proton beam bunch timing using a small liquid scintillator volume was planned, and the safety discussions for the measurement have been done. This report describes the status of the R&D work and the background measurements, in addition to the milestones required before stage-2 approval.

physics.ins-det↗
arXiv2015

On-site Background Measurements for the J-PARC E56 Experiment: A Search for Sterile Neutrino at J-PARC MLF

The J-PARC E56 experiment aims to search for sterile neutrinos at the J-PARC Materials and Life Science Experimental Facility (MLF). In order to examine the feasibility of the experiment, we measured the background rates of different detector candidate sites, which are located at the third floor of the MLF, using a detector consisting of plastic scintillators with a fiducial mass of 500 kg. The result of the measurements is described in this article. The gammas and neutrons induced by the beam as well as the backgrounds from the cosmic rays were measured.

physics.ins-det↗
arXiv2015

DIOS: the dark baryon exploring mission

DIOS (Diffuse Intergalactic Oxygen Surveyor) is a small satellite aiming for a launch around 2020 with JAXA's Epsilon rocket. Its main aim is a search for warm-hot intergalactic medium with high-resolution X-ray spectroscopy of redshifted emission lines from OVII and OVIII ions. The superior energy resolution of TES microcalorimeters combined with a very wide field of view (30--50 arcmin diameter) will enable us to look into gas dynamics of cosmic plasmas in a wide range of spatial scales from Earth's magnetosphere to unvirialized regions of clusters of galaxies. Mechanical and thermal design of the spacecraft and development of the TES calorimeter system are described. We also consider revising the payload design to optimize the scientific capability allowed by the boundary conditions of the small mission.

astro-ph.IM↗
arXiv2015

Status Report (BKG measurement): A Search for Sterile Neutrino at J-PARC MLF

At the 17th J-PARC PAC, which was held on September 2013, we proposed the sterile neutrino search at J-PARC MLF. After reviewing the proposal, PAC recommended to have a background measurement at the detector's candidate site location in their report to investigate whether the background rates can be manageable for the real experiment or not. Therefore, we have performed the background measurements (MLF; 2013BU1301 test experiment) during the summer of 2014, also following the 18th J-PARC PAC recommendations, and the measurements results are described here.

physics.ins-det↗
arXiv2014

ASTRO-H White Paper - New Spectral Features

This white paper addresses selected new (to X-ray astronomy) physics and data analysis issues that will impact ASTRO-H SWG observations as a result of its high-spectral-resolution X-ray microcalorimeter, the focussing hard X-ray optics and corresponding detectors, and the low background soft gamma-ray detector. We concentrate on issues of atomic and nuclear physics, including basic bound-bound and bound-free transitions as well as scattering and radiative transfer. The major topic categories include the physics of charge exchange, solar system X-ray sources, advanced spectral model, radiative transfer, and hard X-ray emission lines and sources.

astro-ph.HE↗
arXiv2014

ASTRO-H White Paper - High Resolution Spectroscopy of Interstellar and Circumgalactic Gas in the Milky Way and Other Galaxies

We describe the potential of high resolution imaging spectroscopy with the SXS on ASTRO-H to advance our understanding of the interstellar- and circumgalactic media of our own Galaxy, and other galaxies. Topics to be addressed range from absorption spectroscopy of dust in the Galactic interstellar medium, to observations to constrain the total mass-, metal-, and energy flow out of starburst galaxies.

astro-ph.HE↗
arXiv2014

Cosmic ray tests of a GEM-based TPC prototype operated in Ar-CF4-isobutane gas mixtures: II

The spatial resolution along the pad-row direction was measured with a GEM-based TPC prototype for the future linear collider experiment in order to understand its performance for tracks with finite projected angles with respect to the pad-row normal. The degradation of the resolution due to the angular pad effect was confirmed to be consistent with the prediction of a simple calculation taking into account the cluster-size distribution and the avalanche fluctuation.

physics.ins-det↗
arXiv2013

Proposal: A Search for Sterile Neutrino at J-PARC Materials and Life Science Experimental Facility

We propose a definite search for sterile neutrinos at the J-PARC Materials and Life Science Experimental Facility (MLF). With the 3 GeV Rapid Cycling Synchrotron (RCS) and spallation neutron target, an intense neutrino beam from muon decay at rest (DAR) is available. Neutrinos come from μ+ decay, and the oscillation to be searched for is (anti νμ-> anti νe) which is detected by the inverse βdecay interaction (anti νe + p -> e+ + n), followed by a gamma from neutron capture. The unique features of the proposed experiment, compared with the LSND and experiments using horn focused beams, are; (1) The pulsed beam with about 600 ns spill width from J-PARC RCS and muon long lifetime allow us to select neutrinos from μDAR only. (2) Due to nuclear absorption of π- and μ-, neutrinos from μ- decay are suppressed to about the $10^{-3}$ level. (3) Neutrino cross sections are well known. The inverse βdecay cross section is known to be a few percent accuracy. (4) The neutrino energy can be calculated from positron energy by adding ~1.8 MeV. (5) The anti νμand νe fluxes have different and well defined spectra. This allows us to separate oscillated signals from those due to μ- decay contamination. We propose to proceed with the oscillation search in steps since the region of Δm^2 to be searched can be anywhere between sub-eV^2 to several tens of eV^2. We start to examine the large Δm^2 region, which can be done with short baseline at first. At close distance to the MLF target gives a high neutrino flux, and allows us to use relatively small detector. If no definitive positive signal is found, a future option exists to cover small Δm^2 region. This needs a relatively long baseline and requires a large detector to compensate for the reduced neutrino flux.

physics.ins-det↗
arXiv2013

Efficient Site-specific Low-energy Electron Production via Interatomic Coulombic Decay Following Resonant Auger Decay

We identified interatomic Coulombic decay (ICD) channels in argon dimers after spectator-type resonant Auger decay $2p^{-1}~3d \to 3p^{-2}3d, 4d$ in one of the atoms, using momentum resolved electron-ion-ion coincidence. The results illustrate that the resonant core excitation is a very efficient way of producing slow electrons at a specific site, which may cause localized radiation damage. We find also that ICD rate for $3p^{-2}4d$ is significantly lower than that for $3p^{-2}3d$.

physics.chem-ph↗
arXiv2012

Search for the decay $B^0\to DK^{*0}$ followed by $D\to K^-π^+$

We report a study of the decay $B^0\rightarrow D K^+π^-$ followed by $D\rightarrow K^-π^+$, where $D$ indicates $D^0$ or $\bar{D}^0$. We reconstruct the $D K^+π^-$ state in a phase space corresponding to $D K^{*}(892)^0$. The CP-violating angle $ϕ_3$ affects its decay rate via the interference between $b\rightarrow u$ and $b\rightarrow c$ transitions. The result is obtained from a 711 ${\rm fb}^{-1}$ data sample that contains 772 $\times 10^6 B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We measure the ratio ${\cal R}_{DK^{*0}} \equiv Γ(B^0\rightarrow [K^-π^+]_DK^+π^-)/Γ(B^0\rightarrow [K^+π^-]_DK^+π^-)$ to be $(4.1 ^{+ 5.6 + 2.8}_{- 5.0 - 1.8}) \times 10^{-2}$, and set an upper limit of ${\cal R}_{DK^{*0}} < 0.16$ at the 95% confidence level.

hep-ex↗
arXiv2012

Thermodynamics, spin-charge separation and correlation functions of spin-1/2 fermions with repulsive interaction

We investigate the low temperature thermodynamics and correlation functions of one-dimensional spin-1/2 fermions with strong repulsion in an external magnetic field via the thermodynamic Bethe ansatz method. The exact thermodynamics of the model in a weak magnetic field is derived with the help of Wiener-Hopf techniques. It turns out that the low energy physics can be described by spin-charge separated conformal field theories of an effective Tomonaga-Luttinger liquid and an antiferromagnetic SU(2) Heisenberg spin chain. However, these two types of conformally invariant low-lying excitations may break down as excitations take place far away from the Fermi points. The long distance asymptotics of the correlation functions and the critical exponents for the model in the presence of a magnetic field at zero temperature are derived in detail by solving dressed charge equations and by conformal mapping. Furthermore, we calculate the conformal dimensions for particular cases of correlation functions. The leading terms of these correlation functions are given explicitly for a weak magnetic field $H\ll 1$ and for a magnetic field close to the critical field $H\rightarrow H_{c}$. Our analytical results provide insights into universal thermodynamics and criticality in one-dimensional many-body physics.

cond-mat.quant-gas↗
arXiv2012

Search for Antihelium with the BESS-Polar Spectrometer

In two long-duration balloon flights over Antarctica, the BESS-Polar collaboration has searched for antihelium in the cosmic radiation with higher sensitivity than any reported investigation. BESS- Polar I flew in 2004, observing for 8.5 days. BESS-Polar II flew in 2007-2008, observing for 24.5 days. No antihelium candidate was found in BESS-Polar I data among 8.4\times 10^6 |Z| = 2 nuclei from 1.0 to 20 GV or in BESS-Polar II data among 4.0\times 10^7 |Z| = 2 nuclei from 1.0 to 14 GV. Assuming antihelium to have the same spectral shape as helium, a 95% confidence upper limit of 6.9 \times 10^-8 was determined by combining all the BESS data, including the two BESS-Polar flights. With no assumed antihelium spectrum and a weighted average of the lowest antihelium efficiencies from 1.6 to 14 GV, an upper limit of 1.0 \times 10^-7 was determined for the combined BESS-Polar data. These are the most stringent limits obtained to date.

astro-ph.CO↗
arXiv2011

Measurement of the cosmic-ray antiproton spectrum at solar minimum with a long-duration balloon flight over Antarctica

The energy spectrum of cosmic-ray antiprotons from 0.17 to 3.5 GeV has been measured using 7886 antiprotons detected by BESS-Polar II during a long-duration flight over Antarctica near solar minimum in December 2007 and January 2008. This shows good consistency with secondary antiproton calculations. Cosmologically primary antiprotons have been investigated by comparing measured and calculated antiproton spectra. BESS-Polar II data show no evidence of primary antiprotons from evaporation of primordial black holes.

astro-ph.HE↗
arXiv2011

Search for CP Violation in D Meson Decays to phi pi+

We search for CP violation in Cabibbo-suppressed charged D meson decays by measuring the difference between the CP violating asymmetries for the Cabibbo-suppressed decays D+ -> K+K-pi+ and the Cabibbo-favored decays Ds -> K+K-pi+ in the K+K- mass region of the phi resonance. Using 955/fb of data collected with the Belle detector we obtain A_CP(D+ -> phi pi+) = (+0.51 +- 0.28 +- 0.05)%. The measurement improves the sensitivity of previous searches by more than a factor of five. We find no evidence for direct CP violation.

hep-ex↗