We report cosmic-ray proton and helium spectra in energy ranges of 1È120 GeV nucleon~1 and 1È54 GeV nucleon~1, respectively, measured by a Ñight 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 Ðeld of 1 T. Those spectra were determined within overall uncertainties of^5% for protons and^10% for helium nuclei including statistical and systematic errors.

We measured low energy cosmic-ray proton and helium spectra in the kinetic energy range 0.215 -21.5 GeV/n at different solar activities during a period from 1997 to 2002. The observations were carried out with the BESS spectrometer launched on a balloon at Lynn Lake, Canada. A calculation for the correction of secondary particle backgrounds from the overlying atmosphere was improved by using the measured spectra at small atmospheric depths ranging from 5 through 37 g/cm 2 . The uncertainties including statistical and systematic errors of the obtained spectra at the top of atmosphere are 5-7% for protons and 6-9% for helium nuclei in the energy range 0.5 -5 GeV/n.

Primary and atmospheric cosmic-ray spectra were precisely measured with the BESS-TeV spectrometer. The spectrometer was upgraded from BESS-98 to achieve seven times higher resolution in momentum measurement. We report absolute fluxes of primary protons and helium nuclei in the energy ranges, 1-540 GeV and 1-250 GeV/n, respectively, and absolute flux of atmospheric muons in the momentum range 0.6-400 GeV/c.

The energy spectrum of cosmic-ray antiprotons (p's) has been measured in the range 0.18 to 3.56 GeV, based on 458p's collected by BESS in recent solar-minimum period. We have detected for the first time a distinctive peak at 2 GeV ofp'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 flights toward the solar maximum will help us to study the solar modulation and the propagation in detail and to search for primaryp components.PACS numbers: 98.70.Sa, 95.85.RyThe origin of cosmic-ray antiprotons (p's) has attracted much attention since their observation was first reported by Golden et al. [1]. Cosmic-rayp's should certainly be produced by the interaction of Galactic high-energy cosmic-rays with the interstellar medium. The energy spectrum of these "secondary"p's is expected to show a characteristic peak around 2 GeV, with sharp decreases of the flux below and above the peak, a generic feature which reflects the kinematics ofp production. The secondaryp's offer a unique probe [2] of cosmic-ray propagation and of solar modulation. As other possible sources of cosmic-rayp's, one can conceive novel processes, such as annihilation of neutralino dark matter or evaporation of primordial black holes [3]. Thep's from these "primary" sources, if they exist, are expected to be prominent at low energies [4] and to exhibit large solar modulations [5]. Thus they are distinguishable in principle from the secondaryp component.The detection of the secondary peak and the search for a possible low-energy primaryp component have been difficult to achieve, because of huge backgrounds and the extremely small flux especially at low energies. The first [1] and subsequent [6] evidence for cosmic-rayp's were reported at relatively high energies, where it was not possible to positively identify thep's with a mass measurement. The first "mass-identified" and thus unambiguous detection of cosmic-rayp's was performed by BESS '93 [7] in the low-energy region (4 events at 0.3 to 0.5 GeV), which was followed by IMAX [8] and CAPRICE [9] detections. The BESS '95 measured the spectrum [10] at solar minimum, based on 43p's over the range 0.18 to 1.4 GeV. We report here a new high-statistics measurement of thep spectrum based on 458 events in the energy 1

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.

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.Comment: 4 pages, 4 figure

The energy spectra of cosmic-ray low-energy antiprotons (p's) and protons (p's) have been measured by BESS in 1999 and 2000, during a period covering the solar field reversal. Based on these measurements, a sudden increase of thep/p flux ratio following the solar field reversal was observed as predicted by a drift model of the solar modulation.PACS numbers: 98.70. Sa, 96.40.Kk, 95.85.Ry The real underlying physics of the sun is the 22 year solar magnetic cycle with recurrent positive and negative phases. The magnetic field polarity flips when the solar activity is maximum and the global magnetic field profile reverses in the heliosphere. The most recent field reversal should happen in the beginning of 2000. The solar modulation of cosmic rays is caused by expanding solar wind, which spreads out locally irregular magnetic field and therefore modifies energy spectra of the cosmic rays entering the heliosphere. The positive and negative particles drift in opposite directions, during their propagation in the large scale heliospheric magnetic field. The charge-sign dependence is, therefore, a natural consequence [1] in the solar modulation, and it explains alternate appearances of "flat" and "peaked" periods in neutron monitor data around solar minima. In spite of an emerging understanding that the drift became unimportant for several years around the solar maximum [2], recent works [3][4][5] indicated that the drift produces a strong differentiation between the positive and negative particles even during the high solar activity. This view is supported by measurements of temporal variation in cosmic-ray ratios, such as electrons to helium nuclei (He) [6] and electrons to protons (p's) [7], where the largest variation is associated with the solar field reversal. Antiprotons (p's) and their ratio to p's may be novel probes to study the solar modulation becausep's differ from p's only in the charge sign while electrons would behave differently from He and p's due to their lighter mass [4].In the last solar minimum period, the BESS experiment revealed that the cosmic-rayp spectrum has a distinct peak around 2 GeV [8], which is a characteristic feature of secondaryp's produced by cosmic-ray interactions with interstellar (IS) gas. It has become evident thatp's are predominantly secondary in origin, because several recent calculations of the secondary spectrum basically agree with observations in their absolute values and spectral shapes [4,5,9,10].We report here new measurements of cosmic-rayp and p fluxes and their ratios in the energy range from 0.18 to 4.2 GeV collected in two BESS balloon flights carried out in 1999 and 2000, when the solar activity was maximum. Based on the solar magnetic field data [11], the Sun's polarity reversed between these two flights [12]. With our full set of data [8,[13][14][15], we observed the temporal variation of thep flux andp/p ratio covering the solar minimum, the maximum, and the field reversal.The BESS spectrometer was designed [16,17] and developed [18-21] as a high-resolution ...

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 paper, we report the antiproton spectrum obtained, discuss the origin of cosmic-ray antiprotons, and use antiproton data to probe the effect of charge-signdependent drift in the solar modulation.