Charmonia formation in quark-gluon plasma

Using the color evaporation model, the cross section for charmonium production in p + p collision is calculated in quark-gluon plasma. The threshold energy for open charms is given by the free-energy potential from lattice calculations, the initial charm quark pairs by the PYTHIA simulations, and their time evolution by solving the Langevin equation. It is found that the threshold energy, which decreases with temperature, reduces the cross sectionwhile the invariant mass of charm pairs which decreases by collisions enhances it. As a result, charmonium production is suppressed by 20%similar to 50% depending on temperature and charm diffusion constant while J / psi production is similar or enhanced compared with in vacuum.