Measurement of associated charm production in W final states at sqrt(s) = 7 TeV

We present a detailed study of the associated production of a W boson and one c-quark jet in pp collisions at a center-of-mass energy of 7 TeV. The analysis has been conducted with a data sample corresponding to a total integrated luminosity of $5~\textrm{fb}^{-1}$, collected by the CMS detector at the LHC. Candidates of W bosons are identified through their decay into a charged lepton (muon or electron) and a neutrino, in the pseudorapidity range $|\eta^{\ell}|<2.1$. The W + c measurements are performed for charm jets in the kinematic region $p_T^{jet}>25$ GeV, $|\eta^{jet}|<2.5$ and for two different thresholds of transverse momentum of the lepton from the W decay. Using hadronic and inclusive semileptonic decays of charm hadrons total cross sections and cross section ratios are measured. Measurements are also done differentially with respect the pseudorapidity of the lepton from the W decay. These results provide important information on the strange and anti-strange quark parton density functions of the proton at the electroweak scale. Results are compared with theoretical predictions at next-to-leading order using different parton distribution function sets. Whereas current theoretical predictions are in agreement with the measured W + c cross sections at the 10\% level, an analysis of data distributions sensitive to W + ccbar and W + bbbar backgrounds reveals large differences between Monte Carlo generators. In particular, simulations based on PYTHIA show a large deficit when compared with experimental observations in some specific kinematic configurations.