Study of $J/\psi$ production in jets

Abstract

The production of $J/\psi$ 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 $J/\psi$ meson, $\mathcal{z}(J/\psi \equiv p_T(J/\psi)/p_T(jet)$, is measured using jets with $p_T$(jet) > 20  GeV in the pseudorapidity range $2.5 < \eta(jet) < 4.0$. The observed $\mathcal{z}(J/\psi)$ distribution for $J/\psi$ mesons produced in b-hadron decays is consistent with expectations. However, the results for prompt $J/\psi$ production do not agree with predictions based on fixed-order nonrelativistic QCD. This is the first measurement of the $p_T$ fraction carried by prompt $J/\psi$ mesons in jets at any experiment.