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

The production of a Vector Boson in association with a single charm quark is measured and presented here using 140 fb−1 of proton–proton collision data collected with the ATLAS detector at the Large Hadron Collider. Measurements are performed using either a Z boson or W boson produced with a charm meson. 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 Z boson is reconstructed from the decay to either a pair of electrons or muons. The reconstruction modes used for charm hadron reconstruction are D+ → K−π+π+ and D∗+ → D0π+ → (K−π+)π+ and the charge conjugate decays. The W+D(∗) 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 fiducial region is defined to include events passing pT(e, μ) > 30 GeV, |η(e, μ)| < 2.5, pT(D(∗)) > 8 GeV, and |η(D(∗))| < 2.2. The measured total fiducial cross-sections are: 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 anti-charm 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. The Z+D(∗) integrated and normalized differential cross-sections as a function of the transverse momentum of the charmed hadron, are extracted from the data using the same fit strategy. The fiducial region is defined to include events passing pT(e, μ) > 27 GeV, |η(e, μ)| < 2.5, pT(D(∗)) > 8 GeV, and |η(D(∗))| < 2.2. The measured total fiducial cross-sections in the Z+D(∗) analysis are σfid(Z0+D±) = 21.9 ± 0.04 (stat.) +1.5−1.4 (syst.) pb, and σfid(Z0+D∗±) =31.1 ± 0.23 (stat.) +1.3 −1.3 (syst.) pb. These results are also compared with the predictions of next-to-leading-order quantum chromodynamics calculations performed using state-of-the art parton distribution functions.