Y. Shikaze

Search for Cosmic-Ray Antideuterons

We performed a search for cosmic-ray antideuterons using data collected during four BESS balloon flights from 1997 to 2000. No candidate was found. We derived, for the first time, an upper limit of 1.9 x 10(-4) (m2s sr GeV/nucleon)(-1) for the differential flux of cosmic-ray antideuterons, at the 95% confidence level, between 0.17 and 1.15 GeV/nucleon at the top of the atmosphere.

Measurement of the cosmic-ray low-energy antiproton spectrum with the first BESS-Polar Antarctic flight

Abstract The BESS-Polar spectrometer had its first successful balloon flight over Antarctica in December 2004. During the 8.5-day long-duration flight, almost 0.9 billion events were recorded and 1,520 antiprotons were detected in the energy range 0.1–4.2 GeV. In this Letter, we report the antiproton spectrum obtained, discuss the origin of cosmic-ray antiprotons, and use antiproton data to probe the effect of charge-sign-dependent drift in the solar modulation.

Measurements of atmospheric muon spectra at mountain altitude

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.

Search for Antihelium with the BESS-Polar Spectrometer

In two long-duration balloon flights over Antarctica, the Balloon-borne Experiment with a Superconducting Spectrometer (BESS) collaboration has searched for antihelium in the cosmic radiation with the highest sensitivity reported. 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 8.4×10(6) |Z|=2 nuclei from 1.0 to 20 GV or in BESS-Polar II data among 4.0×10(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 to the possible abundance of antihelium relative to helium of 6.9×10(-8)} was determined combining all BESS data, including the two BESS-Polar flights. With no assumed antihelium spectrum and a weighted average of the lowest antihelium efficiencies for each flight, an upper limit of 1.0×10(-7) from 1.6 to 14 GV was determined for the combined BESS-Polar data. Under both antihelium spectral assumptions, these are the lowest limits obtained to date.

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.

BESS-Polar: long duration flights at antarctica to search for primordial antiparticles

Abstract The BESS-Polar experiment with long-duration balloon flights at Antarctica aims at extremely sensitive measurement of low energy antiprotons to search for novel primary origins in the early Universe, and to study cosmic-ray propagation and solar modulation. The search for cosmic antimatter is a fundamental objective to study baryon asymmetry in the Universe. The BESS experiment with high rigidity resolution and large geometrical acceptance will maximize advantages of long duration flights at Antarctica where the rigidity cut-off is lowest. A very compact and thin superconducting magnet spectrometer is being developed to maximize the detector performance in low energies. The BESS-Polar project and progress of the development are described.

Measurements of galactic cosmic-ray hydrogen and helium isotopes with the BESS-polar II instrument

Nicolas Picot-Clémente∗†, K. Abe2, H. Fuke3, S. Haino4, T. Hams5, M. Hasegawa4, A. Horikoshi4, A. Itazaki2, K.C. Kim1, T. Kumazawa4, A. Kusumoto2, M.H. Lee1, Y. Makida4, S. Matsuda4, Y. Matsukawa2, K. Matsumoto4, J.W. Mitchell5, A.A. Moiseev5, J. Nishimura1, M. Nozaki4, R. Orito2, J.F. Ormes6, K. Sakai5, M. Sasaki5, E.S. Seo1, Y. Shikaze2, R. Shinoda7, R.E. Streitmatter5, J. Suzuki4, Y. Takasugi2, K. Takeuchi2, K. Tanaka4, N. Thakur6, T. Yamagami4, A. Yamamoto4, T. Yoshida3, K. Yoshimura4 1 Institute for Physical Science and Technology, University of Maryland, College Park MD 20742, USA 2 Kobe University, Kobe, Hyogo 657-8501, Japan 3 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (ISAS/JAXA), Sagamihara, Kanagawa 252-5210, Japan 4 High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan 5 National Aeronautics and Space Administration, Goddard Space Flight Center (NASA/GFSC), Greenbelt, MD 20771, USA 6 University of Denver, Denver, CO 80208, USA 7 The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan

Precise Measurements of Hydrogen and Helium Isotopes with BESS-Polar II

A precise knowledge of cosmic-ray hydrogen and helium isotopes provides important information to better understand Galactic cosmic-ray propagation. Deuteron and helium 3 species are mainly secondary particles created by the spallation of primary proton and helium 4 particles during their propagation in the Galaxy. Secondary-to-primary ratios thus bring direct information on the average amount of material traversed by cosmic rays in the interstellar medium. The Balloon-borne Experiment with Superconducting Spectrometer BESS-Polar II flew over Antarctica for 24.5 days from December 2007 through January 2008, during the 23rd solar cycle minimum. The instrument is made of complementary particle detectors which allow to precisely measure the charge, velocity and rigidity of incident cosmic rays. It can accurately separate and precisely measure cosmic-ray hydrogen and helium isotopes between 0.2 and 1.5 GeV/nucleon. These data, which are the most precise to date, will be reported and their implications will be discussed.

BESS-polar measurements of the cosmic-ray proton and helium spectra

K. Sakai∗1,9†, K. Abe2‡ , H. Fuke3, S. Haino4§ , T. Hams1,9, M. Hasegawa4, A. Horikoshi4, A. Itazaki2, K. C. Kim5, T. Kumazawa4, A. Kusumoto2, M. H. Lee5, Y. Makida4, S. Matsuda4, Y. Matsukawa2, K. Matsumoto4, J. W. Mitchell1, Z. Myers5, J. Nishimura6, M. Nozaki4, R. Orito2¶, J. F. Ormes7, N. Picot-Clemente5, M. Sasaki1,9, E. S. Seo5, Y. Shikaze2, R. Shinoda6, R. E. Streitmatter1, J. Suzuki4, Y. Takasugi2, K. Takeuchi2, K. Tanaka4, N. Thakur1, T. Yamagami3‖, A. Yamamoto4, T. Yoshida3 and K. Yoshimura8 1 NASA-Goddard Space Flight Center (NASA-GSFC), Greenbelt,MD 20771, USA 2 Kobe University, Kobe, Hyogo 657-8501, Japan 3 Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency

BESS-Polar: Search for Antihelium

We have searched for antihelium in cosmic-rays since 1993 using a series of nine conventional BESS northern latitude balloon flights and two long-duration BESS-Polar Antarctic balloon flights. The BESS-Polar spectrometer is an evolutionary development of the previous BESS instruments, adapted to long duration flight. No antihelium candidate was found in the rigidity ranges of 0.6-20 GV among 8 × 10 6 helium nuclei events for BESS-Polar I and in the rigidity range of 0.6-14 GV among 4 × 10 7 events for BESS-Polar II, respectively. A resultant upper limit of 6.9 × 10 −8 for the abundance ratio of antihelium/helium at the top of the atmosphere in the rigidity range of 1-14 GV was set by combining all the BESS and BESS-Polar flight data. This is the most stringent limit obtained to date.