K+production in relativistic heavy-ion collisions

Recent experimental data on $K^{+}$ production at 2.1 GeV/nucleon are not explained by either the cascade model or the fireball model. Here we introduce a hybrid model in which the total kaon yield is given by individual nucleon-nucleon collisions but its momentum distribution is determined by the temperature of the pion. The model is able to explain the data. The possibility of studying $K^{+}$ yield as a signature for the pionic instability in heavy-ion collisions is indicated.