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

We present an improved determination of the upand 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 non-zero iso-spin asymmetry of the sea, x(d̄ − ū), at small values of Bjorken x ∼ 10−4 indicating a delayed onset of the Regge asymptotics of a vanishing (d̄− ū)-asymmetry at small-x. We compare with upand 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.