Upper Limits of p-bar/p Ratio by 10 TeV Cosmic Rays Observed in Tibet

佐々木 孝雄


   The shadows of the Moon and the Sun by the cosmic rays have been detected in the 10 TeV energy region by the Tibet Air Shower Array at the site of an altitude of 4,300 m a.s.l., and 90.52°E, 30.11°N. The Sun shadow using the data obtained in the time period from June 1990 to October 1993 is found with a significance of -5.0 σ at a position of 0.6°or more displaced from the apparent Sun's position to the west. When the deficits for two calender periods of "1990 , 91" and "1992 , 93", and two different sector periods of the "away" and "toward" fields of solar wind are superposed with an appropriate rotation around the apparent Sun's axis, the significance of the Sun shadow increases to -6.2 σ. Because any deficit is not seen at the corresponding position on the opposite side against the real Sun, the upper limit of p/p ratio in the primary cosmic rays is caluculated to be about 16.9 % at energy around 10 TeV, taking account of the contribution of helium with energy 16 TeV to be 19 % at the same dificit position.