"Figure 12b" of "$J/\psi$ production at low $p_T$ in Au+Au and Cu+Cu collisions at $\sqrt{s_{_{NN}}}$ = 200 GeV at STAR"

The $J/\psi$ $p_T$ spectrum and nuclear modification factor ($R_{AA}$) are reported for $p_T$ < 5 GeV/c and |y|<1 from 0% to 60% central Au+Au and Cu+Cu collisions at $\sqrt{s_{NN}}$ = 200 GeV at STAR. A significant suppression of $p_T$-integrated $J/\psi$ production is observed in central Au+Au events. The Cu+Cu data are consistent with no suppression, although the precision is limited by the available statistics. $R_{AA}$ in Au+Au collisions exhibits a strong suppression at low transverse momentum and gradually increases with $p_T$. The data are compared to high-$p_T$ STAR results and previously published BNL Relativistic Heavy Ion Collider results. Comparing with model calculations, it is found that the invariant yields at low $p_T$ are significantly above hydrodynamic flow predictions but are consistent with models that include color screening and regeneration.