Kinetics in Heavy-Ion Collisions*

We investigate the in-medium kinetics of the X(3872) and B_c particles in ultra-relativistic heavy-ion collisions. Toward this end, we employ our well-tested rate equation approach for quarkonia to compute the time evolution of the X(3872) and B_c distributions, each governed by two transport parameters, i.e., the equilibrium limit and inelastic reaction rate. The equilibrium limits of X(3872) and B_c are entirely determined by the particles' masses and the previously calculated charm-quark and bottom-quark fugacities. The reaction rate for the X(3872) is believed to depend on its structure, being "large" for a DD* molecule and "small" for a tetraquark (diquark-antidiquark). The reaction rate of the B_c is calculated in the quasi-free approximation as previously used for charmonia and bottomonia. We evaluate the sensitivity of the final X(3872) abundance and p_T spectra on different scenarios for its width and

initial conditions. We find that the final yields of a loosely bound molecule are generally smaller than for the tetraquark, by around a factor of two. This is qualitatively different from most coalescence model calculations to date. We also present the centrality and transverse-momentum dependence of the B_c R_AA and discuss it in the context of recent CMS experiment data.