The production of a $W$ boson in association with a single charm quark is studied using $140{\mathrm{fb}}^{-1}$ of $\sqrt{s}=13\mathrm{TeV}$ proton-proton collision data collected with the ATLAS detector at the Large Hadron Collider. The charm quark is tagged by the presence of a charmed hadron reconstructed with a secondary-vertex fit. The $W$ boson is reconstructed from the decay to either an electron or a muon and the missing transverse momentum present in the event. The charmed mesons reconstructed are $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$ and $D^{*+}\to D^0{\pi }^{+}\to (K^{-}{\pi }^{+}){\pi }^{+}$ and the charge conjugate decays in the fiducial regions where $p_{\mathrm{T}}(e,\mu )>30\mathrm{GeV}$, $|\eta (e,\mu )|<2.5$, $p_{\mathrm{T}}(D^{(*)})>8\mathrm{GeV}$, and $|\eta (D^{(*)})|<2.2$. The integrated and normalized differential cross sections as a function of the pseudorapidity of the lepton from the $W$ boson decay, and of the transverse momentum of the charmed hadron, are extracted from the data using a profile likelihood fit. The measured total fiducial cross sections are ${\sigma }_{\mathrm{fid}}^{\mathrm{OS}–\mathrm{SS}}(W^{-}+D^{+})=50.2\pm 0.2{(\mathrm{stat})}_{-2.3}^{+2.4}(\mathrm{syst})\mathrm{pb}$, ${\sigma }_{\mathrm{fid}}^{\mathrm{OS}–\mathrm{SS}}(W^{+}+D^{-})=48.5\pm 0.2{(\mathrm{stat})}_{-2.2}^{+2.3}(\mathrm{syst})\mathrm{pb}$, ${\sigma }_{\mathrm{fid}}^{\mathrm{OS}–\mathrm{SS}}(W^{-}+D^{*+})=51.1\pm 0.4{(\mathrm{stat})}_{-1.8}^{+1.9}(\mathrm{syst})\mathrm{pb}$, and ${\sigma }_{\mathrm{fid}}^{\mathrm{OS}–\mathrm{SS}}(W^{+}+D^{*-})=50.0\pm 0.4{(\mathrm{stat})}_{-1.8}^{+1.9}(\mathrm{syst})\mathrm{pb}$. Results are compared with the predictions of next-to-leading-order quantum chromodynamics calculations performed using state-of-the-art parton distribution functions. Additionally, the ratio of charm to anticharm production cross sections is studied to probe the $s\text{−}\overline{s}$ quark asymmetry. The ratio is found to be $R_c^{\pm }=0.971\pm 0.006(\mathrm{stat})\pm 0.011(\mathrm{syst})$. The ratio and cross-section measurements are consistent with the predictions obtained with parton distribution function sets that have a symmetric $s\text{−}\overline{s}$ sea, indicating that any $s\text{−}\overline{s}$ asymmetry in the Bjorken-$x$ region relevant for this measurement is small.

• Received 2 February 2023
• Accepted 1 May 2023

DOI:https://doi.org/10.1103/PhysRevD.108.032012

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.

© 2023 CERN, for the ATLAS Collaboration