The collider experiments at the Tevatron and the LHC will allow for detailed investigations of the properties of the top quark. This requires precise predictions of the hadronic production of t t pairs and of their subsequent decays. In this Letter we present for the reactions p p, pp→tt+X →ℓ+ℓ−+X the first calculation of the dilepton angular distribution at next-to-leading order (NLO) in the QCD coupling, keeping the full dependence on the spins of the intermediate tt state. The angular distribution reflects the degree of correlation of the t and t spins which we determine for different choices of t and t spin bases. In the case of the Tevatron, the QCD corrections are sizeable, and the distribution is quite sensitive to the parton content of the proton.

The quark recombination mechanism is proposed to explain the asymmetry between production rates of D+ and of D− in their inclusive productions, and also asymmetries for other charmed hadrons. These asymmetries are observed in experiment and are called as leading particle effects. In this work we give a general analysis for contributions of quark recombination to these asymmetries. The contributions consist of a perturbative- and nonperturbative part. We perform two types of factorization by considering the produced hadron with large transverse momentum and by taking charm quark as a heavy quark, respectively. In the case of large transverse momentum the effect of quark recombination is the standard twist-4 effect. We find that the contributions are parameterized with four nonperturbative functions, defined with four quark operators at twist-4, for initial hadrons without polarization. By taking charm quark as a heavy quark the factorization can be performed with the heavy quark effective theory(HQET). The effect of quark recombination is in general parameterized by eight nonperturbative parameters which are defined as integrals with matrix elements of four quark operators defined in HQET. For unpolarized hadrons in the initial state, the parameters can effectively be reduced to four. Perturbative parts in the two types of factorization are calculated at tree-level.

In ongoing and upcoming hadron collider experiments, top quark physics will play an important role in testing the Standard Model and its possible extensions. In this work we present analytic results for the differential cross sections of top quark pair production in hadronic collisions at next-to-leading order in the QCD coupling, keeping the full dependence on the spins of the top quarks. These results are combined with the corresponding next-to-leading order results for the decay of polarized top quarks into dilepton, lepton plus jets, and all jets final states. As an application we predict double differential angular distributions which are due to the QCD-induced top quark spin correlations in the intermediate state. In addition to the analytic results, we give numerical results in terms of fit functions that can easily be used in an experimental analysis.