Precise measurements of the cosmic ray antiproton spectrum with BESS including the effects of solar modulation |
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Institution: | 1. NASA, Goddard Space Flight Center, Greenbelt, MD 20771, USA;2. The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan;3. Kobe University, Kobe, Hyogo 657-8501, Japan;4. The University of Maryland, College Park, MD 20742, USA;5. High Energy Accelerator Research Organization (KEK), Tuskuba, Ibaraki 305-0801, Japan;6. Institute of Space and Astronautical Science (ISAS), Sagamihara, Kanagawa 229-8510, Japan |
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Abstract: | The Balloon Borne Experiment with a Superconducting Spectrometer (BESS) has measured the energy spectrum of cosmic-ray antiprotons between 0.18 and 4.20 GeV in eight flights between 1993 and 2002. Above about 1 GeV, models in which antiprotons are secondary products of the interactions of primary cosmic rays with the interstellar gas agree with the BESS antiproton spectrum. Below 1 GeV, the data show a possible excess antiproton flux compared to secondary model predictions, suggesting the presence of an additional source of antiprotons. The antiproton/proton ratios measured between 1993 and 1999, during the Sun’s positive-polarity phase, are consistent with simple models of solar modulation. However, results from the 2000 flight, following the solar magnetic field reversal, show a sudden increase in the antiproton/proton ratio and tend to favor a charge-sign-dependent drift model. To extend BESS measurements to lower energies, an evolutionary instrument, BESS-Polar, is under construction for polar flight in 2004. |
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