We introduce a new string model (venus 2) for ultrarelativistic heavy-ion collisions, based on color exchange between quarks and also between antiquarks. These two mechanisms affect the rapidity distribution of baryons differently: Quark color exchange shifts baryons towards central rapidity, antiquark color exchange moves baryons back towards large (c.m.) rapidities. We obtain almost flat baryon rapidity distributions for symmetric A+A collisions. Rapidity distributions for proton-nucleus collisions show a forward plateau rather than a forward peak, in agreement with data.

• Received 13 February 1989

DOI:https://doi.org/10.1103/PhysRevLett.62.2460