COALESCENCE MODEL FOR DEUTERONS AND ANTIDEUTERONS IN RELATIVISTIC HEAVY-ION COLLISIONS

Existing formulations of the coalescence model for the formation of sm all nuclear clusters in nuclear collisions cannot distinguish between particle and antiparticle clusters and ignore the interactions of the cluster constituents with the other particles in the interaction regio n. Furthermore none of these models is kinematically fully consistent since the problem of energy conservation in the coalescence process is not dealt with directly, but buried in a phenomenological parameter, the ''coalescence radius.'' Studying the simplest case of (anti)deuter on formation, we include the effects on the coalescence rate from inte ractions with the medium, which allow for off-shell propagation and th us for energy conservation during coalescence, via effective medium-de pendent masses for the cluster constituents. Instead of the conceptual ly ill-defined ''coalescence radius'' the width of the mass distributi ons is introduced as a fundamental parameter which, through the scatte ring rate in the medium, can be related to the temperature of the coll ision fireball. The freeze-out condition for the created clusters rela tes the thermodynamical parameters of the fireball to its geometric si ze at freeze-out and thus provides a deeper understanding of the role of the phenomenological ''coalescence radius'' in previous formulation s. It automatically predicts different radius parameters and coalescen ce probabilities for deuterons and antideuterons. A detailed compariso n of our new formulation with previous approaches is given.