$J\mathrm{/}\psi$ Production by Magnetic Excitation of ${\eta }_c$

We compute the probability of $J\mathrm{/}\psi$ production from the interaction between ${\eta }_c$ and the strong magnetic field generated in relativistic heavy ion collisions. The computation is first carried out in the heavy quark effective model, in which the M1 radiative transition is considered. Then we investigate the transition in the framework of non-relativistic heavy hadron chiral perturbation theory and show that the polarization of $J\mathrm{/}\psi$ produced by this process is parallel to the direction of magnetic field and thus perpendicular to the reaction plane. The transition probability obtained in both approaches is of order $2\times {10}^{-4}$.