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The cosmic-ray proton and helium spectra from 0.2 GeV nucleon~1 to about 200 GeV nucleon~1 have been measured with the balloon-borne experiment Isotope Matter-Antimatter Experiment (IMAX) launched from Lynn Lake, Manitoba, Canada, in 1992. IMAX was designed to search for antiprotons and light isotopes using a superconducting magnet spectrometer together with scintillators, a time-of-Ñight system, and Cherenkov detectors. Using redundant detectors, an extensive examination of the instrument efficiency was carried out. We present here the absolute spectra of protons and helium corrected to the top of the atmosphere and to interstellar space. If demodulated with a solar modulation parameter of / \ 750 MV, the measured interstellar spectra between 20 and 200 GV can be represented by a power law in rigidity, with (1.42^0.21) ] 104R~2.71B0.04 (m2 GV s sr)~1 for protons and (3.15^1.03) ] 103R~2.79B0.08 (m2 GV s sr)~1 for helium. Subject headings : cosmic rays È elementary particles È ISM : abundances

Recently the AMS-02 collaboration has published the measurement of the cosmic antiproton to proton ratio ¯ p/p and the ¯ p flux with a high precision up to ∼ 450 GeV. In this work, we perform a systematic analysis of the secondary antiproton flux generated by the cosmic ray interaction with the interstellar gas. The uncertainty of the prediction originates from the cosmic ray propagation process and the hadronic interaction models. Although the cosmic ray propagation parameters have been well controlled by the AMS-02 B/C ratio data for a specified model, different propagation models can not be discriminated by the B/C data. The ¯ p flux is also calculated for several hadronic interaction models, which are generally adopted by the cosmic ray community. However, the results for different hadronic models do not converge. We find the EPOS LHC model, which seems to fit the collider data very well, predicts a slightly lower ¯ p/p ratio than the AMS-02 data at the high energy end. Finally we derive the constraints on the dark matter annihilation cross section from the AMS-02 ¯ p/p ratio for different propagation and hadronic interaction models. PACS numbers: 96.50.S-,95.35.+d

The Isotope Magnet Experiment (ISOMAX), a balloon-borne superconducting magnet spectrometer, was designed to measure the isotopic composition of the light isotopes (3 Z 8) of cosmic radiation up to 4 GeV nucleon À1 with a mass resolution of better than 0.25 amu by using the velocity versus rigidity technique. To achieve this stringent mass resolution, ISOMAX was composed of three major detector systems: a magnetic rigidity spectrometer with a precision drift chamber tracker in conjunction with a three-layer time-of-flight system, and two silica-aerogel Cerenkov counters for velocity determination. A special emphasis of the ISOMAX program was the accurate measurement of radioactive 10 Be with respect to its stable neighbor isotope 9 Be, which provides important constraints on the age of cosmic rays in the Galaxy. ISOMAX had its first balloon flight on 1998 August 4-5 from Lynn Lake, Manitoba, Canada. Thirteen hours of data were recorded during this flight at a residual atmosphere of less than 5 g cm À2 . The isotopic ratio at the top of the atmosphere for 10 Be/ 9 Be was measured to be 0:195 AE 0:036 (statistical) AE 0:039 (systematic) between 0.26 and 1.03 GeV nucleon À1 and 0:317 AE 0:109 (statistical) AE 0:042 (systematic) between 1.13 and 2.03 GeV nucleon À1 . This is the first measurement of its kind above 1 GeV nucleon À1 . ISOMAX results tend to be higher than predictions from current propagation models. In addition to the beryllium results, we report the isotopic ratios of neighboring lithium and boron in the energy range of the time-of-flight system (up to $1 GeV nucleon À1 ). The lithium and boron ratios agree well with existing data and model predictions at similar energies.

Abstract.A measurement of the energy spectra of cosmic-ray positrons and electrons was made with a balloon-borne magnetspectrometer, which was flown at a mean geomagnetic cut-off of 4.5 GV/c. The observed positron flux in the energy range 7-16 GeV is approximately an order of magnitude lower than that of electrons, as measured in other experiments at various energies. The power law spectral index of the observed differential energy spectrum of electrons is −2.89 ± 0.10 in the energy interval 7.5-47 GeV. For positrons the overall fit of the available data above 7 GeV has been considered. The spectral index is found to be −3.37 ± 0.26 and the fraction of positrons, e + /(e + + e − ), has a mean value of 0.064 ± 0.003. The world data on e + /(e + + e − ) from 0.1 to 30 GeV indicate that a plerion type electron spectrum is preferred over the other types. The trend of the presently existing high energy data also suggests a possible contribution of positrons produced at the pulsar polar cap. High resolution experiments capable of identifying positrons at least up to 100 GeV with high statistics are required to pinpoint the origin of both electrons and positrons in the cosmic radiation.

We report new measurements of the muon spectra and the muon charge ratio at ground level in the momentum range from 200 MeV͞c to 120 GeV͞c for two different geomagnetic locations. Above 0.9 GeV͞c the absolute spectra measured in the two locations are in good agreement and are about 10% to 15% lower than previous experimental results. At lower momenta the data show latitude dependent geomagnetic effects. These observations are important for the understanding of the observed neutrino anomaly. PACS numbers: 96.40.Tv, 96.40.Kk, 14.60.PqPrecise measurements of the muon energy spectrum and charge ratio at sea level over a wide energy range provide information on the propagation of cosmic rays in the atmosphere. Together with data on the primary cosmic rays, muon measurements can be used as a test to check calculations of atmospheric cascades and neutrino fluxes [1]. These latter calculations are used to interpret the recent re-

We report on the hydrogen nuclei (protons and deuterons) spectrum from 0.15 to 200 GeV and on the helium nuclei spectrum over the energy range from 0.2 to 100 GeV nucleon~1 at the top of the atmosphere measured by the balloon-borne experiment Cosmic Antiparticle Ring-Imaging Cerenkov Experiment (CAPRICE), which was Ñown from Lynn Lake, Manitoba, Canada, on 1994 August 8È9. We also report on the proton spectrum over the energy range from 0.15 to 4.2 GeV. The experiment used the NMSU-WiZard/CAPRICE balloon-borne magnet spectrometer equipped with a solid radiator RingImaging Cerenkov (RICH) detector and a silicon-tungsten calorimeter for particle identiÐcation. This was the Ðrst time a RICH was used together with an imaging calorimeter in a balloon-borne experiment. These detectors allowed for clear particle identiÐcation, as well as excellent control of the detector efficiencies. The data were collected during 18 hr at a residual mean atmospheric depth of 3.9 g cm~2. With this apparatus 516,463 hydrogen and 32,457 helium nuclei were identiÐed in the rigidity range 0.4 to 200 GV and 1.2 to 200 GV, respectively. The observed energy spectrum at the top of the atmosphere can be represented by (1.1^0

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