Measurement of the production cross section for a W boson in association with a charm quark in proton-proton collisions at $\sqrt{s}$ = 13 TeV

The strange quark content of the proton is probed through the measurement of the production cross section for a W boson and a charm (c) quark in proton-proton collisions at a center-of-mass energy of 13 TeV. The analysis uses a data sample corresponding to a total integrated luminosity of 138 fb$^{-1}$ collected with the CMS detector at the LHC. The W bosons are identified through their leptonic decays to an electron or a muon, and a neutrino. Charm jets are taggedusing the presence of a muon or a secondary vertex inside the jet.The W+c production cross section and the cross section ratio $R_c^{\pm} = \sigma({\rm W^+ + \bar{c}}) / \sigma({\rm W^- + c}) $ are measured inclusively and differentially as functions of the transverse momentum and the pseudorapidity of the lepton originating from the W boson decay.The precision of the measurements has been improved with respect to previous studies, reaching 1% in $R_c^{\pm}$. The measurements are compared with theoretical predictions up to next-to-next-to-leading order in perturbative quantum chromodynamics.