  We simulate the fragmentation processes in the {$\alpha$~$+$~Au~} collisions
at a bombarding energy of 5 GeV/u using the simplified RQMD approach plus the
statistical decay model. We find from the simulation that the
angular-distribution of the intermediate mass fragments has a sideward peak,
more strongly in the transverse direction than in the beam-direction, when the
intermediate nucleus formed by the dynamical process has an annular eclipse
shape, which explains the experimental results.
