K. Kasahara - Academia.edu (original) (raw)

Papers by K. Kasahara

Astroparticle Physics, 2012

Supplement of the …, 1971

This is a publication of results obtained by the collaboration experiment of the Brazil and Japan... more This is a publication of results obtained by the collaboration experiment of the Brazil and Japan Emulsion Group over a period of nearly ten years since 1962. It is divided into five parts. I. Introduction gives a short description of the emulsion chambers exposed at Mt. Chacaltaya Laboratory (5200 m), Bolivia, ranging from Camara No. 1 of 0.4 m 2 up to Camara No. 15 of 44.2 m 2 , with a brief historical review of the collaboration experiment. Main part of the present results are obtained with Camara No. 12 (6m 2) and No. 13 (9.8 m 2), both of which have the producer layer for nuclear interactions in the chamber itself. II. Morphological Studies on Cosmic-ray Components give the results on frequency, energy spectrum and zenith angle distribution of the electromagnetic and the nuclear-active components at Chacaltaya. The vertical flux for the electromagnetic component is (2.66 •10-9 / cm 2 sec sterad)• (E/10 12 eV)-P with ,8=2.07±0.10, covering energy region of 2•10 11 eV~5•10" eV. Ratio of a flux value of the electromagnetic component to that of the nuclear-active component of the same visible energy is ~0.56, constant over the concerned energy region. III. Fire-l-all Studies on C-jets give detailed analysis on 85 events of local nuclear interactions with L:Er~3 TeV occurred in the producer layer. High energy 7-rays produced in the interaction are described in the integral form as Nrexp(-NrEr/L:Er) with Nr=8±1. All of the results on energy spectrum, angular distribution, PT distribution and PT-Or correlation show that those 7-rays are products of an isotropic intermediate state (a fire-ball) with momentum distribution, Nrexp(-p"t/po)(p1/pi)dp"t with Nr=8±1, po=82±15MeV in its rest system. A fire-ball analysis is made on individual 75 C-jets with the observed 7-ray multiplicity equal to or greater than 4. Seventy one events are found to show emission of a fire-ball. Their experimental mass spectrum has a peak at IDlr~1.2 GeV, giving the average value as <IDlr)=1.28±0.35 GeV where Wlr is a part of the rest energy liberated into 7-rays. IV. Atmospheric Interactions be concemsed with analysis on 41 7-ray families which are * This number is obtained from a part of the chamber which was analyzed in INS (Tokyo), Campinas Univ. and CBPF of Rio de Janeiro. Once the energy measurement is made on all detected individual r-rays constituting the C-jet, one can apply the method of coupling of a pair of rrays into n°-meson in order to estimate a location of its production in the producer layer. Their average height is estimated as

A possible origin of the large-scale anisotropy of TeV galactic cosmic rays is discussed. It can ... more A possible origin of the large-scale anisotropy of TeV galactic cosmic rays is discussed. It can be well modeled by a superposition of the Global Anisotropy and the Midscale Anisotropy. The Global Anisotropy would be generated by galactic cosmic rays interacting with the magnetic field in the local interstellar space of a few parsec scale surrounding the heliosphere. On the other hand, the Midscale Anisotropy would be caused by the modulation of galactic cosmic rays in the heliotail. The Midscale Anisotropy can be expressed as two intensity enhancements placed along the Hydrogen Deflection Plane, each symmetrically centered away from the heliotail direction. It is found that the separation angle between the heliotail direction and each of the two intensity enhancements monotonously decreases as energy increases from 4 TeV to 30 TeV.

Physical Review D, 2004

We have revised the calculation of the flux of atmospheric neutrinos based on a 3-dimensional sch... more We have revised the calculation of the flux of atmospheric neutrinos based on a 3-dimensional scheme with the realistic IGRF geomagnetic model. The primary flux model has been revised, based on the AMS and BESS observations, and the interaction model updated to DPMJET-III. With a fast simulation code and computer system, the statistical errors in the Monte Carlo study are negligible. We estimate the total uncertainty of the atmospheric neutrino flux prediction is reduced to 10 % below 10 GeV. The '3-dimensional effects' are found to be almost the same as the study with the dipole magnetic field, but the muon curvature effect remains up to a few tens of GeV for horizontal directions. The uncertainty of the absolute normalization of the atmospheric neutrino is still large above 10 GeV due to the uncertainty of the primary cosmic ray flux above 100 GeV. However, the zenith angle variation is not affected by these uncertainties.

Physical Review Letters, 2013

We report on a clear solar-cycle variation of the Sun's shadow in the 10 TeV cosmic-ray flux obse... more We report on a clear solar-cycle variation of the Sun's shadow in the 10 TeV cosmic-ray flux observed by the Tibet air shower array during a full solar cycle from 1996 to 2009. In order to clarify the physical implications of the observed solar cycle variation, we develop numerical simulations of the Sun's shadow, using the potential field source surface (PFSS) model and the current sheet source surface (CSSS) model for the coronal magnetic field. We find that the intensity deficit in the simulated Sun's shadow is very sensitive to the coronal magnetic field structure, and the observed variation of the Sun's shadow is better reproduced by the CSSS model. This is the first successful attempt to evaluate the coronal magnetic field models by using the Sun's shadow observed in the TeV cosmic-ray flux.

As the first result of the Tibet experiment the data obtained during the week centered at the rad... more As the first result of the Tibet experiment the data obtained during the week centered at the radio-burst from Cygnus X-3 on 15th of August, 1990, were analysed. But the preliminary results do not give any excess from Cygnus X-3 in this period at the median energy 30 TeV.

Physical Review D, 1982

... K. Mizutani Depa. rtment ofPhysics, Saitama University, Saitama, Japan K. Kasahara, S. Torii,... more ... K. Mizutani Depa. rtment ofPhysics, Saitama University, Saitama, Japan K. Kasahara, S. Torii, and T. Yuda Institute for Cosmic Ray Research, Uniuersity of Tokyo, Tokyo, Japan T. Shirai, N. Tateyama, and T. Taira Faculty ofEngineering, Kanagawa Uniuersity, yokohama, Japan ...

Nuclear Physics B - Proceedings Supplements, 2014

A Monte Carlo simulation was carried out to investigate the characteristic features of large gamm... more A Monte Carlo simulation was carried out to investigate the characteristic features of large gamma-ray families. In addition to the energy flux and multiplicity spectra, the mean spread of constituent gamma-rays of the family is discussed in connection with the average transverse momentum of secondary gamma rays for various models and primary energy spectra. Some remarks are made on the

LHCf is a collider experiment dedicated to obtaining information relevant to ultra-high-energy co... more LHCf is a collider experiment dedicated to obtaining information relevant to ultra-high-energy cosmic-ray physics. One of the two LHCf detectors has position-sensitive silicon microstrip layers that are read out with front end electronics. These electronics saturate for high energy photon showers because of the limited dynamic range of the preamplifier. Consequently we are planning an upgrade of the processing circuits in anticipation of LHC operation at increased collision energy, and we are developing an analysis method to correct for the saturation effect. An overview of these data analysis methods will be given in this paper.

LHCf is a small detector installed at LHC accelerator to measure neutral particle flow in the for... more LHCf is a small detector installed at LHC accelerator to measure neutral particle flow in the forward direction of proton-proton (p-p) and proton-nucleus (p-A) interactions. Thanks to the optimal performance that has characterized the last years' running of the LHC collider, several measurements have been taken since 2009 in different running conditions. After data taking for p-p interactions at √ s = 900 GeV, 2.76 TeV and 7 TeV and proton-Lead nucleus (p-Pb) at √ s NN = 5.02 TeV (energy of a couple of projectile and target nucleons in their center of mass reference frame), LHCf is now going to complete its physics program with the 13 TeV p-p run foreseen in 2015. The complete set of results will become a reference data set of forward physics for the calibration and tuning of the hadronic interaction models currently used for the simulation of the atmospheric showers induced by very high energy cosmic rays. For this reason we think that LHCf is giving an important contribution for the study of cosmic rays at the highest energies. In this paper the experiment, the published results and the current status are reviewed.

We are developing the CALET mission to observe high energy cosmic rays at the Japanese Experiment... more We are developing the CALET mission to observe high energy cosmic rays at the Japanese Experiment Module/Exposed Facility (JEM/EF) on the International Space Station. The instrument will be flown in 2013, and will be used for 5 years. The primary scientific purpose of CALET is to search for nearby cosmic ray sources and dark matter. We carried out an accelerator beam test with high energy particles with the CALET prototype at the CERN-SPS. The purpose of this test was to assess the detector performance as well as to study the accuracy of the Monte Carlo simulation method. The prototype detector consists of an imaging calorimeter with 256 scintillating fibers and a total absorption calorimeter consisting of 16 PWO logs. The longitudinal structure is similar with the CALET instrument. We used positron and proton beams in the energy region from 6 to 200 GeV, and from 30 to 150 GeV, respectively. Comparing the experimental data with the simulation results, we have measured the energy deposition in each component, the energy resolution, the lateral shower spread and the e/p separation capability.

We have operated the 500 m 2 Yangbajing air-shower core (YAC-II) detector array near the center o... more We have operated the 500 m 2 Yangbajing air-shower core (YAC-II) detector array near the center of the Tibet air-shower array (Tibet-III) to study the cosmic-ray chemical composition at the knee energy region since August, 2011. YAC-II array consists of 124 YAC detector units. Each unit of YAC-II consists of a lead layer of 3.5 cm thick and a scintillation counter which detects the burst size induced by high energy electromagnetic component in the air-shower cores. Each scintillator has the size 80 cm × 50 cm × 1 cm. 60 WLSFs (Wave Length Shifting Fiber) are installed inside the scintillator, a high-gain PMT and a low-gain PMT are coupled with it. The burst size can be measured from 1 MIP (Minimum Ionization Particles) to 10 6 MIPs. In this paper, the details of the hybrid experiment and the processes of the data reconstruction are described.

The Astrophysical Journal, 2009

The Tibet-III air shower array, consisting of 533 scintillation detectors, has been operating suc... more The Tibet-III air shower array, consisting of 533 scintillation detectors, has been operating successfully at Yangbajing in Tibet, China since 1999. Using the dataset collected by this array from 1999 November through 2005 November, we obtained the energy spectrum of γ-rays from the Crab Nebula, expressed by a power law as (dJ/dE) = (2.09 ± 0.32) × 10 −12 (E/3 TeV) −2.96±0.14 cm −2 s −1 TeV −1 in the energy range of 1.7 to 40 TeV. This result is consistent with other independent γ-ray observations by imaging air Cherenkov telescopes. In this paper, we carefully checked and tuned the performance of the Tibet-III array using data on the moon's shadow in comparison with a detailed Monte Carlo simulation. The shadow is shifted to the west of the moon's apparent position as an effect of the geomagnetic field, although the extent of this displacement depends on the primary energy positively charged cosmic rays. This finding enables us to estimate the systematic error in determining the primary energy from its shower size. This error is estimated to be less than ±12% in our experiment. This energy scale estimation is the first attempt among cosmic-ray experiments at ground level. The systematic pointing error is also estimated to be smaller than 0. • 011. The deficit rate and position of the moon's shadow are shown to be very stable within a statistical error of ±6% year by year. This guarantees the long-term stability of point-like source observation with the Tibet-III array. These systematic errors are adequately taken into account in our study of the Crab Nebula. Subject headings: cosmic rays-gamma rays : observations-magnetic fields-Moon-pulsars : individual (Crab pulsar)-supernova remnants : individual (Crab Nebula)

Science, 2006

The intensity of Galactic cosmic rays is nearly isotropic due to the influence of magnetic fields... more The intensity of Galactic cosmic rays is nearly isotropic due to the influence of magnetic fields in the Milky Way. Here we present two-dimensional highprecision anisotropy measurement for energies from a few to several hundred TeV using the huge data sample of the Tibet Air Shower Arrays. Besides revealing finer details of the known anisotropies, a new component of sidereal time Galactic cosmic ray anisotropy is uncovered around the Cygnus region direction. For cosmic-ray energies up to a few hundred TeV, all components of anisotropies fade away, showing a corotation of Galactic cosmic rays with the local Galactic magnetic environment. These results bear broad implications to cosmic rays, supernovae, magnetic field, heliospheric and Galactic dynamic environment in a comprehensive manner.