Observation of the production of a W soson in association with a single charm quark

The first observation of the production of a W boson with a single charm quark (c) jet in pp¯ collisions at s√=1.96  TeV is reported. The analysis uses data corresponding to 4.3  fb−1, recorded with the CDF II detector at the Fermilab Tevatron. Charm quark candidates are selected through the identification of an electron or muon from charm-hadron semileptonic decay within a hadronic jet, and a Wc signal is observed with a significance of 5.7 standard deviations. The production cross section σWc(pTc>20  GeV/c,|ηc| 0.71 at the 95% confidence level, assuming that the Wc production through c to s quark coupling is dominant.