# Study of $J/\psi$ production in jets

## TL;DR

This paper measures the fraction of jet momentum carried by $J/$ mesons in proton-proton collisions at 13 TeV, revealing discrepancies with theoretical predictions for prompt production.

## Contribution

First measurement of the $p_T$ fraction of prompt $J/$ mesons in jets at any experiment, providing new insights into quarkonium production mechanisms.

## Key findings

- $z$ distribution for $J/$ from $b$-hadron decays matches expectations.
- Prompt $J/$ results do not align with fixed-order non-relativistic QCD predictions.
- First such measurement at any experiment.

## 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, $z \equiv p_{\rm T}(J/\psi)/p_{\rm T}({\rm jet})$, is measured using jets with $p_{\rm T}({\rm jet}) > 20$ GeV in the pseudorapidity range $2.5 < \eta({\rm jet}) < 4.0$. The observed $z$ 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 non-relativistic QCD. This is the first measurement of the $p_{\rm T}$ fraction carried by prompt $J/\psi$ mesons in jets at any experiment.