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Featured researches published by T. Sonoda.


The Astrophysical Journal | 2000

Precise Measurement of Cosmic-Ray Proton and Helium Spectra with the BESS Spectrometer

T. Sanuki; M. Motoki; H. Matsumoto; E. S. Seo; J. Z. Wang; K. Abe; K. Anraku; Y. Asaoka; M. Fujikawa; M. Imori; T. Maeno; Y. Makida; N. Matsui; H. Matsunaga; J. W. Mitchell; T. Mitsui; A. Moiseev; J. Nishimura; Mitsuaki Nozaki; S. Orito; J. F. Ormes; T. Saeki; Makoto Sasaki; Y. Shikaze; T. Sonoda; R. E. Streitmatter; J. Suzuki; Kazunobu Tanaka; I. Ueda; N. Yajima

We report cosmic-ray proton and helium spectra in energy ranges of 1-120 GeV nucleon-1 and 1-54 GeV nucleon-1, respectively, measured by a flight of the Balloon-borne Experiment with Superconducting Spectrometer (BESS) in 1998. The magnetic rigidity of the cosmic ray was reliably determined by highly precise measurement of the circular track in a uniform solenoidal magnetic field of 1 T. Those spectra were determined within overall uncertainties of ±5% for protons and ±10% for helium nuclei including statistical and systematic errors.


Physical Review Letters | 2000

Precision Measurement of Cosmic-Ray Antiproton Spectrum

S. Orito; T. Maeno; H. Matsunaga; K. Abe; K. Anraku; Y. Asaoka; M. Fujikawa; M. Imori; M. Ishino; Y. Makida; N. Matsui; H. Matsumoto; John W. Mitchell; T. Mitsui; A. Moiseev; M. Motoki; J. Nishimura; Mitsuaki Nozaki; J. F. Ormes; T. Saeki; T. Sanuki; M. Sasaki; E. S. Seo; Y. Shikaze; T. Sonoda; R. E. Streitmatter; J. Suzuki; Kazunobu Tanaka; I. Ueda; N. Yajima

The energy spectrum of cosmic-ray antiprotons ( &pmacr;s) has been measured in the range 0.18-3.56 GeV, based on 458 &pmacr;s collected by BESS in a recent solar-minimum period. We have detected for the first time a characteristic peak at 2 GeV of &pmacr;s originating from cosmic-ray interactions with the interstellar gas. The peak spectrum is reproduced by theoretical calculations, implying that the propagation models are basically correct and that different cosmic-ray species undergo a universal propagation. Future BESS data with still higher statistics will allow us to study the solar modulation and the propagation in detail and to search for primary &pmacr; components.


Physical Review Letters | 2002

Measurements of cosmic-ray low-energy antiproton and proton spectra in a transient period of solar field reversal.

Y. Asaoka; Y. Shikaze; K. Abe; K. Anraku; M. Fujikawa; H. Fuke; S. Haino; M. Imori; K. Izumi; T. Maeno; Y. Makida; S. Matsuda; N. Matsui; T. Matsukawa; H. Matsumoto; H. Matsunaga; J. Mitchell; Takahisa Mitsui; A. Moiseev; M. Motoki; J. Nishimura; Mitsuaki Nozaki; S. Orito; J. F. Ormes; T. Saeki; T. Sanuki; Makoto Sasaki; Eul Soo Seo; T. Sonoda; R.E. Streitmatter

The energy spectra of cosmic-ray low-energy antiprotons ( *ps) and protons ( ps) have been measured by BESS in 1999 and 2000, during a period covering reversal at the solar magnetic field. Based on these measurements, a sudden increase of the *p/p flux ratio following the solar magnetic field reversal was observed, and it generally agrees with a drift model of the solar modulation.


Astroparticle Physics | 2001

Successive measurements of cosmic-ray antiproton spectrum in a positive phase of the solar cycle

T. Maeno; S. Orito; H. Matsunaga; K. Abe; K. Anraku; Y. Asaoka; M. Fujikawa; M. Imori; Y. Makida; N. Matsui; H. Matsumoto; J. W. Mitchell; T. Mitsui; A. Moiseev; M. Motoki; J. Nishimura; Mitsuaki Nozaki; J. F. Ormes; T. Saeki; T. Sanuki; M. Sasaki; E. S. Seo; Y. Shikaze; T. Sonoda; R. E. Streitmatter; J. Suzuki; Kazunobu Tanaka; I. Ueda; J. Z. Wang; N. Yajima

Abstract The energy spectrum of cosmic-ray antiprotons ( p s) has been measured by BESS successively in 1993, 1995, 1997 and 1998. In total, 848 p s were clearly identified in energy range 0.18–4.20 GeV. From these successive measurements of the p spectrum at various solar activity, we discuss about the effect of the solar modulation and the origin of cosmic-ray p s. The p / p ratios showed no distinctive year-to-year variation during the positive Suns polarity phase.


Astroparticle Physics | 2003

Precise measurements of atmospheric muon fluxes with the BESS spectrometer

M. Motoki; T. Sanuki; S. Orito; K. Abe; K. Anraku; Y. Asaoka; M. Fujikawa; H. Fuke; S. Haino; M. Imori; K. Izumi; T. Maeno; Y. Makida; N. Matsui; H. Matsumoto; H. Matsunaga; John W. Mitchell; T. Mitsui; A. Moiseev; J. Nishimura; Mitsuaki Nozaki; J. F. Ormes; T. Saeki; M. Sasaki; E. S. Seo; Y. Shikaze; T. Sonoda; R.E. Streitmatter; J. Suzuki; K. Tanaka

The vertical absolute fluxes of atmospheric muons and muon charge ratio have been measured precisely at different geomagnetic locations by using the BESS spectrometer. The observations had been performed at sea level (30 m above sea level) in Tsukuba, Japan, and at 360 m above sea level in Lynn Lake, Canada. The vertical cutoff rigidities in Tsukuba (36.2°N, 140.1°E) and in Lynn Lake (56.5°N, 101.0°W) are 11.4 and 0.4 GV, respectively. We have obtained vertical fluxes of positive and negative muons in a momentum range from 0.6 to 20 GeV/c with systematic errors <3% in both measurements. By comparing the data collected at two different geomagnetic latitudes, we have seen an effect of cutoff rigidity. The dependence on the atmospheric pressure and temperature, and the solar modulation effect have been also clearly observed. We also clearly observed the decrease of charge ratio of muons at low momentum side with at higher cutoff rigidity region.


Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment | 2000

Large-area scintillator hodoscope with 50 ps timing resolution onboard BESS

Y. Shikaze; S. Orito; T. Mitsui; K. Yoshimura; H. Matsumoto; H. Matsunaga; Mitsuaki Nozaki; T. Sonoda; I. Ueda; Teppei Yoshida

Abstract We describe the design and performance of a large-area scintillator hodoscope onboard the BESS rigidity spectrometer; an instrument with an acceptance of 0.3 m 2 sr . The hodoscope is configured such that 10 and 12 counters are, respectively, situated in upper and lower layers. Each counter is viewed from its ends by 2.5 in. fine-mesh photomultiplier tubes placed in a stray magnetic field of 0.2 T. Various beam-test data are presented. Use of cosmic-ray muons at ground-level confirmed 50 ps timing resolution for each layer, giving an overall time-of-flight resolution of 70 ps rms using a pure Gaussian-resolution function. Comparison with previous measurements on a similar scintillator hodoscope indicates good agreement with the scaling law that timing resolution is proportional to 1/ N pe , where N pe is the effective number of photoelectrons.


Physics Letters B | 2002

Measurements of atmospheric muon spectra at mountain altitude

T. Sanuki; M. Fujikawa; K. Abe; K. Anraku; Y. Asaoka; H. Fuke; S. Haino; M. Imori; Keisuke Izumi; T. Maeno; Y. Makida; N. Matsui; H. Matsumoto; H. Matsunaga; M. Motoki; J. Nishimura; Mitsuaki Nozaki; S. Orito; M. Sasaki; Y. Shikaze; T. Sonoda; J. Suzuki; Kazunobu Tanaka; Y. Toki; A. Yamamoto; Yasuchika Yamamoto; K. Yamato; T. Yoshida; K. Yoshimura

We report new measurements of absolute fluxes of atmospheric muons at mountain altitude. The measurements were carried out with the BESS detector at the top of Mt. Norikura, 2 770 m above sea level, in Japan. The overall errors were less than 10%. The measured results are discussed in comparison with theoretical calculations.


Advances in Space Research | 2002

Bess and its future prospect for polar long duration flights

A. Yamamoto; K. Abe; K. Anraku; Y. Asaoka; M. Fujikawa; H. Fuke; S. Haino; M. Imori; K. Izumi; T. Maeno; Y. Makida; N. Matsui; H. Matsumoto; H. Matsunaga; F. B. McDonald; J. W. Mitchell; T. Mitsui; A. Moiseev; M. Motoki; J. Nishimura; Mitsuaki Nozaki; S. Orito; J.F. Ormes; D. Righter; T. Saeki; T. Sanuki; M. Sasaki; E. S. Seo; Y. Shikaze; T. Sonoda

Abstract The Balloon-borne Experiment with a Superconducting Spectrometer, BESS, aims to study elementary particle/antiparticle phenomena in the early history of the Universe. The instrument has a unique feature of a thin superconducting solenoid magnet enabling a large geometrical acceptance with a horizontally cylindrical configuration. Seven balloon flights have been successfully carried out since 1993. More than 10 3 comic-ray antiproton have been unambiguously detected, and the energy spectrum has been measured with the characteristic peak at 2 GeV. The search for cosmic-ray antihelium brought the upper-limit of the antihelium/helium ratio down to −6 . To extend the highly sensitive measurements, we are planning polar long duration flights in Antarctica focusing on the very low energy antiproton spectrum towards the solar-minimum in the next decade.


Nuclear Physics B - Proceedings Supplements | 2002

Progress in Search for Antihelium with BESS

M. Sasaki; H. Matsumoto; Mitsuaki Nozaki; T. Saeki; Kanji Abe; K. Anraku; Y. Asaoka; M. Fujikawa; H. Fuke; M. Imori; S. Haino; K. Izumi; T. Maeno; Y. Makida; S. Matsuda; N. Matsui; Tsuyoshi Matsukawa; H. Matsunaga; J. W. Mitchell; Takahisa Mitsui; A. A. Moiseev; M. Motoki; J. Nishimura; S. Orito; J.F. Ormes; T. Sanuki; Y. Shikaze; E. S. Seo; T. Sonoda; R. E. Streitmatter

We have searched for antihelium nuclei in cosmic rays using the data obtained from balloon flights of the BESS magnetic spectrometer. The search was mainly based on track-quality selection, followed by rigidity analysis, and on the time-of-flight and dE/dx measurements by the scintillation counter hodoscope. We analysed all the data collected during 1993–2000 with a common analysis procedure. No antihelium nuclei events were found in the energy range from 1 to 14 GV. In order to determine a new upper limit, we have simulated the loss in the air and in the instrument of He (He) using the GEANT/GHEISHA code. Combined with the data collected in 1993 through 2000, a new 95 % confidence upper limit for the ratio of He/He at the top of the atmosphere of 6.8 × 10−7 has been obtained to be after correcting for the interactions in the air and in the instruments.


Nuclear Instruments & Methods in Physics Research Section A-accelerators Spectrometers Detectors and Associated Equipment | 2002

Measurement of low-energy antiproton detection efficiency in BESS below 1 GeV

Y. Asaoka; K. Yoshimura; T. Yoshida; K. Abe; K. Anraku; M. Fujikawa; H. Fuke; S. Haino; Kosuke Izumi; T. Maeno; Y. Makida; N. Matsui; H. Matsumoto; H. Matsunaga; M. Motoki; Mitsuaki Nozaki; S. Orito; T. Sanuki; M. Sasaki; Y. Shikaze; T. Sonoda; J. Suzuki; Kazunobu Tanaka; Y. Toki; A. Yamamoto

Abstract An accelerator experiment was performed using a low-energy antiproton beam to measure antiproton detection efficiency of BESS, a balloon-borne spectrometer with a superconducting solenoid. Measured efficiencies showed good agreement with calculated ones derived from the BESS Monte Carlo simulation based on GEANT/GHEISHA . With detailed verification of the BESS simulation, the relative systematic error of detection efficiency derived from the BESS simulation has been determined to be ±5%, compared with the previous estimation of ±15% which was the dominant uncertainty for measurements of cosmic-ray antiproton flux.

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