Anisotropy of Subthreshold {ital K}{sup +} Emission in Heavy Ion Reactions
The origin of the forward-backward enhancement of K{sup +} emission observed in symmetric nucleus-nucleus collisions at 1GeV/nucleon has been explored. The nonisotropic pion-baryon reaction leading to K{sup +} production has been found to play a substantial role in creating the forward-backward peak of the kaon angular distribution. By an analysis including also the effects from relevant final-state interactions on kaons, we can reproduce the experimental kaon angular distribution. We argue that the observed nonisotropic kaon emission may provide a support to the pion-induced channel for subthreshold kaon production in heavy ion reactions. {copyright} {ital 1997} {ital The American Physical Society}