[en] We discuss the production of two hadrons in e⁺e^- annihilation within the framework of perturbative QCD. The cross section for this process is calculated to next-to-leading order accuracy with a selection of variables that allows the consideration of events where the two hadrons are detected in the same jet. In this configuration we contemplate the possibility that the hadrons come from a double fragmentation of a single parton. The double-fragmentation functions required to describe the transition of a parton to two hadrons, are also necessary to completely factorize all collinear singularities. We explicitly show that factorization applies to order α_s in the case of two-hadron production

[en] We consider the transverse-momentum (q_T) distribution of Higgs bosons produced at hadron colliders. We use a formalism that uniformly treats both the small-q_T and large-q_T regions in QCD perturbation theory. At small q_T (q_T<< M_H, M_H being the mass of the Higgs boson), we implement an all-order resummation of logarithmically-enhanced contributions up to next-to-next-to-leading logarithmic accuracy. At large q_T (q_T > or approx. M_H), we use fixed-order perturbation theory up to next-to-leading order. The resummed and fixed-order approaches are consistently matched by avoiding double-counting in the intermediate-q_T region. In this region, the introduction of unjustified higher-order terms is avoided by imposing unitarity constraints, so that the integral of the q_T spectrum exactly reproduces the perturbative result for the total cross section up to next-to-next-to-leading order. Numerical results at the LHC are presented. These show that the main features of the q_T distribution are quite stable with respect to perturbative QCD uncertainties

[en] In the present work we produce polarized distributions from the unpolarized ones by using the spin dilution functions which are adjusted in order to fit Emc and SMC data. We also take into account the gluon distribution, which in the dilution model framework is related to an unpolarized gluon distribution g(x) by Δg(s,Q²) = f_g(x,Q²)g(x,Q²) where f_g(x,Q²) is the spin dilution function for the gluon

[en] We present results on the quark and gluon polarization in the nucleon obtained in a combined next to leading order analysis to the available inclusive and semi-inclusive polarized deep inelastic scattering data. Using the Lagrange multiplier method, we assess the uncertainty inherent to the extraction of the different spin dependent parton densities in a QCD global fit, and the impact of the increased set of semi-inclusive data now available. (author)

[en] We investigate the sea quark polarization in the nucleon by means of a combined next to leading order analysis to the recently enlarged set of inclusive and semi-inclusive polarized deep inelastic scattering data. Using the Lagrange multiplier method, we assess the uncertainty inherent to the extraction of the different spin-dependent parton densities in a QCD global fit and the impact of the increased set of semi-inclusive data now available. We comment on future prospects at Relativistic Heavy Ion Collider and the Thomas Jefferson National Laboratory and their potential impact in the future determination of polarized parton densities

[en] We analyze the order alpha_s² corrections to the single inclusive jet and hadron cross sections in lepton-nucleon deep inelastic scattering. The full calculations are done analytically, obtaining finite NLO partonic level cross sections for these processes. We show that in both cases the dominant partonic mechanism starts at order alpha_s², being effectively a lowest order estimate, with the consequent large factorization scale uncertainty, and the likelihood of non-negligible corrections at the subsequent order in perturbation theory. (author)

[en] We present results on the quark and gluon polarization in the nucleon obtained in a combined next to leading order analysis to the available inclusive and semi-inclusive polarized deep inelastic scattering data

[en] We present a general purpose Monte Carlo program for the calculation of any infrared safe observable in Wγ and Zγ production at hadron colliders at next-to-leading order in α_s. We treat the leptonic decays of the W and Z-boson in the narrow-width approximation, but retain all spin information via decay angle correlations. The effect of anomalous triple gauge boson couplings is investigated and we give the analytical expressions for the corresponding amplitudes. Furthermore, we propose a way to study the effect of anomalous couplings without introducing the ambiguity of form factors. (orig.)

[en] We perform a next to leading order QCD global analysis of nuclear deep inelastic scattering and Drell-Yan data using the convolution approach to parametrize nuclear parton densities. We find both a significant improvement in the agreement with data compared to previous extractions, and substantial differences in the scale dependence of nuclear effects compared to leading order analyses

[en] We calculate next to leading order QCD corrections to semi-inclusive polarized deep inelastic scattering and e⁺e^- annihilation cross sections for processes where the polarization of the identified final-state hadron can also be determined. Using dimensional regularization and the HVBM prescription for the γ₅ matrix, we compute corrections for different spin-dependent observables, both in the MS and MS_p factorization schemes, and analyse their structure. In addition to the well-known corrections to polarized parton distributions, we also present those for final-state polarized fracture functions and polarized fragmentation functions, in a consistent factorization scheme. (orig.)