Study of $J\mathrm{/}\psi$ production in jets

The production of $J\mathrm{/}\psi$ mesons in jets is studied in the forward region of proton-proton collisions using data collected with the LHCb detector at a center-of-mass energy of 13 TeV. The fraction of the jet transverse momentum carried by the $J\mathrm{/}\psi$ meson, $z \equiv p_{\rm T}(J/\psi)/p_{\rm T}({\rm jet})$,ismeasuredusingjetswith$p_{\rm T}({\rm jet}) > 20$ GeV in the pseudorapidity range $2.5<\eta (\mathrm{j}\mathrm{e}\mathrm{t})<4.0$. The observed $z$ distribution for $J\mathrm{/}\psi$ mesons produced in $b$-hadron decays is consistent with expectations. However, the results for prompt $J\mathrm{/}\psi$ production do not agree with predictions based on fixed-order non-relativistic QCD. This is the first measurement of the $p_{\mathrm{T}}$ fraction carried by prompt $J\mathrm{/}\psi$ mesons in jets at any experiment.