Measurement of $J/ψ$-jet correlations in $pp$ and Pb+Pb collisions at $\sqrt{s_{\text{NN}}}=5.02$ TeV with the ATLAS detector

Abstract

Yields of charmonia, bound states of $c\bar{c}$ quarks, are observed to be strongly suppressed in heavy-ion collisions relative to proton-proton collisions as a result of their interaction with the quark-gluon plasma produced in such collisions. Understanding the mechanisms responsible for this suppression requires a detailed understanding of charmonium production. To constrain the production mechanisms, it is essential to quantify how charmonium production correlates with jet activity. Measurements of $J/ψ$ production in the dimuon decay channel are presented for inclusive $J/ψ$ mesons and for $J/ψ$ mesons that are either isolated or not isolated from jets, separately for prompt and non-prompt production. Non-isolated $J/ψ$ mesons are defined by matching $J/ψ$ candidates to anti-$k_t$ jets with $R=0.2$ and $p_\mathrm{T}>20$ GeV, reconstructed without signal from the $J/ψ$ meson, allowing the quantification of jet activity accompanying $J/ψ$ production. The analysis uses Pb+Pb and $pp$ collisions at $\sqrt{s_{\text{NN}}}=5.02$ TeV recorded by the ATLAS experiment at the LHC, corresponding to integrated luminosities of 1.82 nb$^{-1}$ and 0.26 fb$^{-1}$, respectively. The $J/ψ$ yields in Pb+Pb, cross sections in $pp$, and nuclear modification factors are presented for non-isolated, isolated, and inclusive $J/ψ$ up to $p_\mathrm{T}=60$ GeV. Isolated fractions and non-prompt fractions are reported in both $pp$ and Pb+Pb collisions. Strong $J/ψ$ suppression is observed to persist up to the highest measured $p_\mathrm{T}$ values, with differences observed between non-isolated, isolated, and inclusive $J/ψ$. These results provide new constraints on charmonium production mechanisms and their in-medium suppression.