Increase of the K+/π+ Ratio Induced by Collective Effects in Relativistic Heavy-Ion Collisions

The collective effects on the increase of the K+/π+ ratio in relativistic heavy-ion collisions are analyzed with the excited nucleon model. The gradual increase of the K+/π+ ratio from p-Be to p-Au to the Si-Au central collisions may be explained self-consistently by multiscattering and secondary hadron collisions without requiring the formation of the quark gluon plasma.