Isospin asymmetry of quark distributions and implications for single top-quark production at the LHC

We present an improved determination of the up-and down-quark distributions in the proton using recent data on charged lepton asymmetries from W-+/- gauge-boson production at the LHC and Tevatron. The analysis is performed in the framework of a global fit of parton distribution functions. The fit results are consistent with a nonzero isospin asymmetry of the sea, x((d) over bar - (u) over bar), at small values of Bjorken x similar to 10(-4) indicating a delayed onset of the Regge asymptotics of a vanishing ((d) over bar - (u) over bar)-asymmetry at small x. We compare with up-and down-quark distributions available in the literature and provide accurate predictions for the production of single top-quarks at the LHC, a process which can serve as a standard candle for the light quark flavor content of the proton.