Critical Scattering at the Chiral Phase Transition and low-p_t enhancement of mesons in ultra-relativistic heavy-ion collisions

The enhancement of pions and kaons observed at small transverse momenta in ultra-relativistic heavy-ion collisions may at least partly reflect critical scattering expected to occur in the neighborhood of a second order phase transition. Kinetic equations in the relaxation time approximation are proposed for the time evolution of the quark distribution function into that of the pions. Relaxation times for thermalization and hadronization processes are functions of momenta and approach zero in the limit p->0, a consequence of criticality at the phase transition. Data can be reproduced for suitably chosen parameters.