L. Meng

Direct evidence of the interplanetary magnetic field effect on the cosmic ray shadow by the sun

The Tibet air-shower array, being successively operated at an altitude of 4300 m above sea level since 1990, has detected the shadows of the Sun and Moon in the 10 TeV cosmic-ray flux. In particular, the shadow of the Sun was observed in the direction significantly away from the apparent solar position, under the influence of the solar and interplanetary magnetic fields. A further analysis shows that the shadows by cosmic rays coming from the away and toward field sectors in the interplanetary space are shifted in opposite directions to one another according to the polarity of the fields. This is the first direct observation of the influence of the interplanetary magnetic field on the shadows displacement

Status and performance of the AS array of the Tibet ASγ experiment

The Tibet ASγ experiment, which has started since January, 1990, is located at an altitude of 4,300m at Yangbaging in Tibet, China (90.5° E, 301° N). The air‐shower array is composed of 49 scintillation counters for fast timing (FT), each counter having an area of 0.5 m2, in a grid pattern with a spacing of 15 m and 16 density detectors. The density detectors surrounding the FT detectors are planned to select the showers of which core are inside the FT array. For the constant and continuous opeation, the system for laser calibration, the ADC,TDC module calibration and the power check system were installed. A Rb clock is used for the phase analysis of γ‐rays.The array is usually operated by the trigger rate of ∼20Hz with any 4‐fold coincidence of the FT detectors. The analysis of experimental data shows that the performance of array is realized as expected by the Monte Carlo simulation. For the events of which core are inside the FT array, are obtained the following results. The detection threshold energy ...