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

The associated production of a W boson with a single charm quark is studied using 140 fb⁻¹ of pp collision data at √s = 13 TeV 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, and the W boson is reconstructed with the decay to either an electron or a muon and missing transverse energy present in the event. The charm mesons reconstructed are D⁺ → K⁻π⁺π⁺ and D^+∗ → D⁰π⁺ → (K⁻π⁺)π⁺ (including 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 charm hadron are extracted from the data using a profiled likelihood fit. These results are compared to the predictions of next-to-leading-order quantum chromodynamics calculations obtained using up-to-date parton distribution function parameterizations. Additionally, the cross-section ratio of charm to anti-charm production cross-sections is studied to probe the s– ¯s quark asymmetry. This analysis gives insight into parton distribution functions and whether an asymmetric s- ¯s sea, in the Bjorken-x region x ∼ 0.1, is supported by the result.