T. Kumazawa

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.

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.

Performance of an ultra-thin superconducting solenoid for particle astrophysics

An extremely thin superconducting solenoid with a main diameter of 0.9 m and a length of 1.4 m has been fabricated for a balloon borne experiment in Antarctica to study anti-particles in cosmic rays. The solenoid has a 0.8 m diameter warm bore where a magnetic field of 0.8-1.0 T is induced. The coil was wound with mechanically advanced aluminum stabilized superconductor recently developed by using micro-alloying Ni into a pure aluminum base and by cold-work hardening, and consequently the electromagnetic force may be fully supported by the coil itself without any additional support structure. The solenoid was successfully charged up to 1.05 T without any premature quenches. Despite measured strains were beyond 1500 micro-strain, the coil behaved elastically. Because of relatively small RRR of 110, the quench energy is distributed rather unevenly, and a temperature difference of over 100 K was observed. Nevertheless, it was found to be safe to quench the magnet.

Ballooning of an Ultra-Thin Superconducting Solenoid for Particle Astrophysics in Antarctica

An ultra-thin superconducting solenoid has been developed to provide a magnetic field of 0.8 T in a balloon-borne spectrometer for cosmic ray research, which is named BESS-Polar. The coil with a diameter of 0.9 m, a length of 1.4 m and a thickness of 3.5 mm was fabricated by using a mechanically strengthened aluminum stabilized superconductor. The coil winding is strong enough to eliminate the outer support cylinder which is necessary in the former thin solenoid type coils. Consequently the coil weight and material thickness are 40 kg, and 2.52 g/cm2, respectively. The BESS-Polar was launched near the US McMurdo Station in Antarctica on December 13th 2004, floated at an altitude of 37000 m around the South Pole for nine days. The solenoid was charged up on the ground and kept the field in a persistent current mode during launch and floating. This report describes the flight performance of the solenoid

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

Search for Novel Origins of Cosmic-ray Antiprotons and Antimatter with BESS-Polar Flight over Antarctica.

The primary aims of the BESS-Polar program are precise measurements of the low-energy antiproton spectrum and search for cosmologically significant antimatter, which would provide new clues to understand the early Universe. The second flight (BESS-Polar II) over Antarctica was successfully carried out in Dec 2007 Jan 2008. We performed 24.5days scientific observation just at the solar minimum. The payload worked well during the flight and 4.7 billion cosmic-ray events were collected. Based on the BESS-Polar II data, we present recent preliminary results of cosmic-ray antiproton measurements and sensitive search for antimatter. 35th International Conference of High Energy Physics ICHEP2010, July 22-28, 2010 Paris France

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.