# $J/\psi$ production and polarization within a jet

## TL;DR

This paper investigates the production and polarization of $J/\psi$ mesons within jets at the LHC, proposing new observables to distinguish production mechanisms and constrain theoretical models.

## Contribution

It introduces the $J/\psi$-jet fragmentation function and suggests measuring $J/\psi$ polarization inside jets to better understand quarkonium production.

## Key findings

- The $J/\psi$-jet fragmentation function effectively probes production mechanisms.
- Measuring $J/\psi$ polarization inside jets can provide additional constraints.
- The proposed observables can differentiate between NRQCD fits.

## Abstract

We study the production and polarization of $J/\psi$ mesons within a jet in proton-proton collisions at the LHC. We define the $J/\psi$-jet fragmentation function as a ratio of differential jet cross sections with and without the reconstructed $J/\psi$ in the jet. We demonstrate that this is a very useful observable to help explore the $J/\psi$ production mechanism, and to differentiate between different NRQCD global fits based on inclusive $J/\psi$ cross sections. Furthermore, we propose to measure the polarization of $J/\psi$ mesons inside the jet, which can provide even more stringent constraints for the heavy quarkonium production mechanism.