Events containing a $Z$ boson and a charm jet are studied for the first time in the forward region of proton-proton collisions. The data sample used corresponds to an integrated luminosity of $6{\mathrm{fb}}^{-1}$ collected at a center-of-mass energy of 13 TeV with the LHCb detector. In events with a $Z$ boson and a jet, the fraction of charm jets is determined in intervals of $Z$-boson rapidity in the range $2.0<y(Z)<4.5$. A sizable enhancement is observed in the forwardmost $y(Z)$ interval, which could be indicative of a valencelike intrinsic-charm component in the proton wave function.

• Received 17 September 2021
• Revised 17 December 2021
• Accepted 28 January 2022

DOI:https://doi.org/10.1103/PhysRevLett.128.082001

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

© 2022 CERN, for the LHCb Collaboration