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 production of a 𝑊 boson in association with a single charm quark is studied using 140  fb⁻¹ of √𝑠=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 𝐷⁺→𝐾⁻⁢𝜋^+⁢𝜋⁺ and 𝐷^*+→𝐷⁰⁢𝜋⁺→(𝐾⁻⁢𝜋⁺)⁢𝜋⁺ and the charge conjugate decays in the fiducial regions where 𝑝_T⁡(𝑒,𝜇)>30  GeV, |𝜂⁡(𝑒,𝜇)|<2.5, 𝑝_T⁡(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 𝜎^OS–SS _fid⁢(𝑊⁻+𝐷⁺)=50.2±0.2⁢(stat)^+2.4_−2.3⁢(syst)  pb, 𝜎^OS–SS_fid
⁢(𝑊⁺+𝐷⁻)=48.5±0.2⁢(stat)^+2.3_−2.2⁢(syst)  pb, 𝜎^OS–SS_fid⁢(𝑊⁻+𝐷^*+)=51.1±0.4⁢(stat)^+1.9−_1.8⁢(syst)  pb, and 𝜎^OS–SS_fid⁢(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.