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