Abstract
The production of a W boson in association with a single charm quark is studied using 140 fb−1 of pffiffi
s 1⁄4 13 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 Dþ → K−πþπþ and D þ →
D0πþ → ðK−πþÞπþ and the charge conjugate decays in the fiducial regions where pTðe; μÞ > 30 GeV,
jηðe;μÞj<2.5, pTðDð ÞÞ>8GeV, and jηðDð ÞÞj<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 σOS–SSðW− þ DþÞ 1⁄4 50.2 0.2ðstatÞþ2.4ðsystÞ pb, fid −2.3
σOS–SSðWþ þ D−Þ 1⁄4 48.5 0.2ðstatÞþ2.3ðsystÞ pb, σOS–SSðW− þ D þÞ 1⁄4 51.1 0.4ðstatÞþ1.9ðsystÞ pb, fid −2.2 fid −1.8
and σOS–SSðWþ þ D−Þ 1⁄4 50.0 0.4ðstatÞþ1.9ðsystÞ pb. Results are compared with the predictions of fid −1.8
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-s ̄ quark asymmetry. The ratio is found to be Rc 1⁄4 0.971 0.006ðstatÞ 0.011ðsystÞ. The ratio and cross-section measurements are consistent with the predictions obtained with parton distribution function sets that have a symmetric s-s ̄ sea, indicating that any s-s ̄ asymmetry in the Bjorken-x region relevant for this measurement is small.