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

A bstract: Yields of charmonia, bound states of $$ c\overline{c} $$ c 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 _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 $$ \sqrt{s_{\mathrm{NN}}}=5.02 $$ s 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 _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 _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.