Measurement of the production of a W boson in association with a charmed hadron in pp collisions at √s=13TeV with the ATLAS detector

The production of a W boson in association with a single charm quark is studied using 140 fb−1 of √s=13TeV 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+→K−π+π+ and D*+→D0π+→(K−π+)π+ and the charge conjugate decays in the fiducial regions where pT(e,μ)>30  GeV, |η(e,μ)|<2.5, pT(D(*))>8 GeV, and |η(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 σOS–SSfid(W−+D+)=50.2±0.2(stat)+2.4−2.3(syst) pb, σOS–SSfid(W++D−)=48.5±0.2( stat)+2.3−2.2(syst)  pb,σOS–SSfid(W−+D*+)=51.1±0.4(stat)+1.9−1.8(syst)  pb, and σOS–SSfid(W++D*−)=50.0±0.4(stat)+1.9−1.8(syst)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−¯s quark asymmetry. The ratio is found to be R±c=0.971±0.006(stat)±0.011(syst). 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.