Tibet AS-gamma Experiment

Present status of our research activities:

Correlation between solar activities and time variation of "the Sun's shadow" in the galactic cosmic rays:

As a charged particle is bent by a magnetic field, the apparent position of the Sun's shadow in the galactic cosmic rays shifts from its expected location due to the solar and interplanetary magnetic fields. Figure 14 demonstrates the yearly variation of "the Sun's shadow" position and the amount of deficit in cosmic rays detected by our air shower array. One can see that the shadow center shifts from its true postion in 1991 and 1992 during which the Sun was in a very active phase, while the Sun's shadow center was on the true position and the event deficit was much more conspicuous in 1996 and 1997 during which the Sun was in a quiescent phase. Our air shower array is capable of such observation exclusively in the world. It is expected that this experiment will provide important data to study the global structure of the solar and interplanetary magnetic fields correlated with 11-year-period solar activities.

Fig. 14 Fig. 15
Fig. 14 Yearly variation of "the Sun's shadow". Each figure represents a contour map of the weights of deficit event densities around the SUN centered at the figure. The contour lines are drawn from a level of no deficit, 0 sigma, with a step of 1 sigma. The mode energy is 10 TeV for the Tibet-I & II arrays and 3 TeV for the Tibet-III array, respectively. Fig. 15 Time variation of interplanetary magnetic field observed by the IMP-8 satellite at the Earth orbit.