An Upper Limit on Cosmic-Ray overline p/p Flux Ratio Estimated by the Moon's Shadow with the Tibet-III Air Shower Array

Details An Upper Limit on Cosmic-Ray overline p/p Flux Ratio Estimated by the Moon's Shadow with the Tibet-III Air Shower Array An Upper Limit on Cosmic-Ray overline p/p Flux Ratio Estimated by the Moon's Shadow with the Tibet-III Air Shower Array

Jul 2003

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003icrc....3.1651a&link_type=abstract

Proceedings of the 28th International Cosmic Ray Conference. July 31-August 7, 2003. Trukuba, Japan. Under the auspices of the I

Physics

Scientific paper

The Tibet air shower array has been in operation since 1999 as TibetI I I (22, 050 m2 ) with energy threshold of a few TeV. As primary cosmic rays are shielded by the moon having the finite size of 0.5o in diameter, we observe a deficit in cosmic rays called the moon's shadow with statistical significance of 32σ . The center of the moon's shadow shifts westwardly due to the geomagnetic field. By analyzing this energy-dep endent westward displacement carefully, we set an upper limit of 11% at 90% confidence level on the cosmic-ray antiproton/proton ratio at multi-TeV energies. 2. Introduction Cosmic antiprotons are mainly produced by collisions of cosmic-ray protons with interstellar hydrogen gas: p+ p-→ p+ p+ p+ p. Accelerator experiments measured the antiproton/proton ratio (R(p/p)) to be about 10-3 ˜ 10-4 in this process. The energy spectrum of the parent cosmic-ray protons has a power-law index ˜ -2.7 above 10 GeV and the power-law index of pshould also be ˜ -2.7. According to a pure secondary production model during the propagation of cosmic rays in the galaxy, R(p/p) decreases as E -0.6 above 10 GeV. Various experimental

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