$\psi(2S)$ photoproduction in high energy nuclear collisions

We study coherent photoproduction of $\psi'$ and the subsequent suppression in high energy nuclear collisions. The hot medium effect on charmonium photoproduction is controlled by the competition between the fireball size and nuclear size. When the former is smaller than the later, the photoproduction is only slightly affected by the hot medium. We calculate the yield ratio of $\psi'$ to $J/\psi$ in semi-central Pb-Pb collisions at LHC energy, while the high $p_T$ limit is characterized by the fireball, its value in low $p_T$ limit can still reach the significant enhancement by photoproduction.