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

Existing formulations of the coalescence model for the formation of small 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 region. 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)deuteron formation, we include the effects on the coalescence rate from interactions with the medium, which allow for off-shell propagation and thus for energy conservation during coalescence, via effective medium-dependent masses for the cluster constituents. Instead of the conceptually ill-defined ''coalescence radius'' the width of the mass distributions is introduced as a fundamental parameter which, through the scattering rate in the medium, can be related to the temperature of the collision fireball. The freeze-out condition for the created clusters relates the thermodynamical parameters of the fireball to its geometric size at freeze-out and thus provides a deeper understanding of the role of the phenomenological ''coalescence radius'' in previous formulations. It automatically predicts different radius parameters and coalescence probabilities for deuterons and antideuterons. A detailed comparison of our new formulation with previous approaches is given.