Hadronic $J/\psi$ Regeneration in Pb+Pb Collisions

TL;DR

This study investigates the regeneration of $J/\psi$ mesons during the hadronic phase of Pb+Pb collisions at the LHC, showing that a significant fraction of observed yields can originate from late-stage hadronic interactions.

Contribution

It introduces a schematic model of hadronic interactions to estimate $J/\psi$ regeneration, providing bounds on the initial production fraction after hadronization.

Findings

$J/\psi$ yields are consistent with 25% to 110% of the initial yield due to regeneration.

The fractional abundance of $J/\psi$ immediately after hadronization is bounded between 0.28 and 1.13.

Regeneration during hadronic phase is significant and must be included in modeling.

Abstract

We make use of published yields for $D$-mesons and $J/\psi$ 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 $J/\psi$ 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 $J/\psi$ immediately after hadronization: $0.28 \leq \frac{dN_0^{J/\psi}/dy}{dN_{\rm eq}^{J/\psi}/dy} \leq 1.13$. 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.