Delineating parton distributions and the strong coupling

Abstract

Global fits for precision determinations of parton distributions, together with the highly correlated strong coupling $\alpha_s$, are presented up to next-to-next-to-leading order (NNLO) of QCD utilizing most world data (charm and jet production data are used where theoretically possible), except TeVatron gauge boson production data and LHC data which are left for genuine predictions. This is done within the `dynamical' (valencelike input at $Q_0^2=0.8$ GeV$^2$) and `standard' (input at $Q_0^2=2$ GeV$^2$) approach. The stability and reliability of the results are ensured by including nonperturbative higher-twist terms, nuclear corrections as well as target mass corrections, and by applying various ($Q^2,W^2$) cuts on available data. In addition, the $Q_0^2$ dependence of the results is studied in detail. Predictions are given, in particular for LHC, on gauge and Higgs boson as well as for top-quark pair production. At NNLO the dynamical approach results in $\alpha_s(M_Z^2)=0.1136\pm0.0004$, whereas the somewhat less constrained standard fit gives $\alpha_s(M_Z^2)=0.1162\pm0.0006$.