Study of $J/\psi\to\mu^+\mu^-$ and $\psi\mathrm{(2S)}\to\mu^+\mu^-$ production with 2015 \PbPb data at $\sqrt{s_{\mathrm{NN}}} = 5.02~\mathrm {TeV}$ and \pp data at $\sqrt{s} = 5.02~\mathrm {TeV}$ with the ATLAS detector

A measurement of $J/\psi$ and $\psi(2\mathrm{S})$ production is presented. It is based on data from lead-lead collisions at $\sqrt{s_{\mathrm{NN}}} = 5.02~\mathrm {TeV}$ and $\textit{pp}$ collisions at $\sqrt{s} = 5.02~\mathrm {TeV}$ recorded by the ATLAS detector at the LHC in 2015, corresponding to integrated luminosity of $0.49~\mathrm{nb}^{-1}$ and $25~\mathrm{pb}^{-1}$ in Pb+Pb and $\textit{pp}$, respectively. The measurements of differential cross sections, nuclear modification factors, and non-prompt fractions were performed in the dimuon decay channel. A strong suppression was found for both prompt and non-prompt $J/\psi$, as well as for prompt and non-prompt $\psi(2\mathrm{S})$, increasing with increasing event centrality. The suppression of prompt $\psi(2\mathrm{S})$ was observed to be stronger than that of $J/\psi$, while the suppression of non-prompt $\psi(2\mathrm{S})$ was equal to that of the non-prompt $J/\psi$ within uncertainties, consistent with the expectation that both arise from $\textit{b}$-quarks propagating through the medium. The dependence of nuclear modification factors with centrality for prompt and non-prompt $J/\psi$ was found to have a similar form, despite the quite different physical origins expected to have given rise to their production: a composite meson formed within the medium and a $\textit{b}$-quark propagating through and out of the medium, respectively.