Hadronic $J/ψ$ Regeneration in Pb+Pb Collisions

Abstract

We make use of published yields for $D$-mesons and $J/ψ$ in Pb+Pb collisions at ALICE and a schematic description of the expansion of the hadron gas to study $D$-meson collisions during the hadronic break-up phase as a production mechanism for charmonium in relativistic heavy ion collisions at the Large Hadron Collider. Our calculation is based on chemical reaction rates with thermal cross sections for an effective meson interaction among pseudoscalar and vector mesons. We find that due to regeneration, the newly measured $J/ψ$ yields are consistent with anywhere from roughly $25\%$ to $110\%$ of the total yield present at hadronization time. This allows us to bound the fractional abundance of $J/ψ$ immediately after hadronization: $0.28 \leq \frac{dN_0^{J/ψ}/dy}{dN_{\rm eq}^{J/ψ}/dy} \leq 1.13$. Our results are robust under the relaxation of the particulars of our schematic description and imply that it will be difficult to distinguish regeneration during hadronization from regeneration by final-state hadronic interactions. Therefore, regeneration must be taken into account when modelling.