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.

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

The cosmic-ray hydrogen and helium spectra have been measured by the Balloon Borne Experiment with a Superconducting Solenoid Spectrometer (BESS), which has been Ñown from Lynn Lake, Manitoba, Canada, annually since 1993. The BESS experiment provides excellent rigidity measurement and precise particle identiÐcation with a large geometric acceptance. We present here the hydrogen and helium nuclei energy spectra from 0.2 to 10 GeV nucleon~1 and their isotopic composition from 0.2 to about 1 GeV nucleon~1 for the Ðrst BESS Ñight. This provides the Ðrst simultaneous measurements of the cosmic-ray secondaries, deuterons, and 3He, with their primaries, protons, and 4He over this energy range in a period of solar minimum. In this paper, we have achieved signiÐcant improvements in data analysis in the following aspects. First, the latest available cross-section data and their parameterizations were utilized in the simulation code developed for this study. Second, a complete simulation was performed for both protons and heavy ions : the d-ray e †ect was properly simulated and showed a large inÑuence on the measurement of heavy ions at high energies. Third, the secondary particle correction, which dominates the systematic uncertainty at low energies for singly charged particles, protons and deuterons, was calculated iteratively with the simultaneously measured primary cosmic-ray spectra. In general, the results of this experiment are consistent with other recent measurements using balloon-borne or satellite experiments, but with better precision. The measured spectra of protons, deuterons, 3He, and 4He and their corresponding ratios are compared with di †erent interstellar/heliospheric propagation calculations, which were derived to Ðt observations of heavy nuclei. The overall good agreement indicates that the propagation history for light cosmic-ray elements, protons, deuterons, and helium nuclei is similar to that of the heavy nuclei. The 2H/1H ratio is sensitive to the propagation models, and our results show a tendency of better agreement with the reacceleration model than the standard leaky-box model.