Canonical Effect on Quarkonium Enhancement in the Deconfined Medium

Studying strong interactions at finite temperatures has been a critical topic in high-energy nuclear collisions. Charmonium, as a clear probe of deconfined matter, is believed to be predominantly influenced by the coalescence of off-diagonal charm and anti-charm quarks. The grand canonical ensemble is commonly used to describe the coalescence of charm and anti-charm quarks. In collisions where only one or two charm pairs are produced, the contribution from the coalescence of diagonal charm and anti-charm quarks becomes dominant, a phenomenon known as the canonical effect. This effect is sensitive to the momentum correlation between the heavy quark and anti-quark. In this work, we employ the Langevin model to study the evolutions of correlated charm and anti-charm quarks and their coalescence process. The asymmetry in the momentum of charm and anti-charm quarks play important roles in their coalescence process. In addition, we investigate the impact of this effect on the nuclear modification factor of charmonium, which can be enhanced evidently in semi-central collisions at RHIC Au-Au collisions. The theoretical calculations with canonical effect explain the experimental data well, which helps us to understand the production mechanisms of the quarkonium bound state in the deconfined medium.