We study the relevance of experimental data on heavy-flavor [$D^0$, $J/\mathrm{<ruby><rb>\psi </rb><rt>ぷさい</rt></ruby>}$, $B\to J/\mathrm{<ruby><rb>\psi </rb><rt>ぷさい</rt></ruby>}$ and $\mathrm{\Upsilon }(1S)$ mesons] production in proton-lead collisions at the LHC to improve our knowledge of the gluon-momentum distribution inside heavy nuclei. We observe that the nuclear effects encoded in both most recent global fits of nuclear parton densities at next-to-leading order (nCTEQ15 and EPPS16) provide a good overall description of the LHC data. We interpret this as a hint that these are the dominant ones. In turn, we perform a Bayesian-reweighting analysis for each particle data sample which shows that each of the existing heavy-quark(onium) data set clearly points—with a minimal statistical significance of $7\mathrm{<ruby><rb>\sigma </rb><rt>しぐま</rt></ruby>}$—to a shadowed gluon distribution at small $x$ in the lead. Moreover, our analysis corroborates the existence of gluon antishadowing. Overall, the inclusion of such heavy-flavor data in a global fit would significantly reduce the uncertainty on the gluon density down to $x\simeq 7\times {10}^{-6}$—where no other data exist—while keeping an agreement with the other data of the global fits. Our study accounts for the factorization-scale uncertainties which dominate for the charm(onium) sector.

• Received 20 December 2017
• Revised 26 April 2018

DOI:https://doi.org/10.1103/PhysRevLett.121.052004

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.

Published by the American Physical Society