We consider higher-order QCD corrections to the production of colourless highmass systems (lepton pairs, vector bosons, Higgs bosons, . . . ) in hadron collisions. We propose a new formulation of the subtraction method to numerically compute arbitrary infrared-safe observables for this class of processes. To cancel the infrared divergences, we exploit the universal behaviour of the associated transverse-momentum (q T ) distributions in the small-q T region. The method is illustrated in general terms up to the next-to-next-to-leading order (NNLO) in QCD perturbation theory. As a first explicit application, we study Higgs boson production through gluon fusion. Our calculation is implemented in a parton level Monte Carlo program that includes the decay of the Higgs boson in two photons. We present selected numerical results at the LHC.

We consider the transverse-momentum (q T ) distribution of generic high-mass systems (lepton pairs, vector bosons, Higgs particles, ....) produced in hadron collisions. At small q T , we concentrate on the all-order resummation of the logarithmicallyenhanced contributions in QCD perturbation theory. We elaborate on the b-space resummation formalism and introduce some novel features: the large logarithmic contributions are systematically exponentiated in a process-independent form and, after integration over q T , they are constrained by perturbative unitarity to give a vanishing contribution to the total cross section. At intermediate and large q T , resummation is consistently combined with fixed-order perturbative results, to obtain predictions with uniform theoretical accuracy over the entire range of transverse momenta. The formalism is applied to Standard Model Higgs boson production at LHC energies. We combine the most advanced perturbative information available at present for this process: resummation up to next-to-next-to-leading logarithmic accuracy and fixed-order perturbation theory up to next-to-leading order. The results show a high stability with respect to perturbative QCD uncertainties.

We consider QCD corrections to Higgs boson production through gluon-gluon fusion in hadron collisions. We compute the cross section, performing the all-order resummation of multiple soft-gluon emission at next-to-next-to-leading logarithmic level. Known fixed-order results (up to next-to-next-to-leading order) are consistently included in our calculation. We give phenomenological predictions for Higgs boson production at the Tevatron and at the LHC. We estimate the residual theoretical uncertainty from perturbative QCD contributions. We also quantify the differences obtained by using the presently available sets of parton distributions.

We study the infrared behaviour of tree-level QCD amplitudes and we derive infrared-factorization formulae that are valid at any perturbative order. We explicitly compute all the universal infrared factors that control the singularities in the various soft and/or collinear limits at O(α 2 S ).(2) § The case of incoming partons can be recovered by simply crossing the parton indices (flavours, spins and colours) and momenta.

We consider QCD radiative corrections to the production of W and Z bosons in hadron collisions. We present a fully exclusive calculation up to next-to-next-to-leading order (NNLO) in QCD perturbation theory. To perform this NNLO computation, we use a recently proposed version of the subtraction formalism. The calculation includes the γ-Z interference, finite-width effects, the leptonic decay of the vector bosons and the corresponding spin correlations. Our calculation is implemented in a parton level Monte Carlo program. The program allows the user to apply arbitrary kinematical cuts on the final-state leptons and the associated jet activity, and to compute the corresponding distributions in the form of bin histograms. We show selected numerical results at the Tevatron and the LHC. March 2009The production of W and Z bosons in hadron collisions through the Drell-Yan (DY) mechanism [1] is extremely important for physics studies at hadron colliders. These processes have large production rates and offer clean experimental signatures, given the presence of at least one highp T lepton in the final state. Studies of the production of W bosons at the Tevatron lead to precise determinations of the W mass and width [2]. The DY process is also expected to provide standard candles for detector calibration during the first stage of the LHC running.Because of the above reasons, it is essential to have accurate theoretical predictions for the vector-boson production cross sections and the associated distributions. Theoretical predictions with high precisions demand detailed computations of radiative corrections. The QCD corrections to the total cross section [3] and to the rapidity distribution [4] of the vector boson are known up to the next-to-next-to-leading order (NNLO) in the strong coupling α S . The fully exclusive NNLO calculation, including the leptonic decay of the vector boson, has been completed more recently [5]. Full electroweak corrections at O(α) have been computed for both W [6] and Z production [7].In this Letter we present a new computation of the NNLO QCD corrections to vector boson production in hadron collisions. The calculation includes the γ-Z interference, finite-width effects, the leptonic decay of the vector bosons and the corresponding spin correlations. Our calculation parallels the one recently completed for Higgs boson production [8,9], and it is performed by using the same method.The evaluation of higher-order QCD corrections to hard-scattering processes is complicated by the presence of infrared (IR) singularities at intermediate stages of the calculation that prevents a straightforward implementation of numerical techniques. Despite this difficulty, general methods have been developed in the last two decades, which allow us to handle and cancel IR singularities [10,11,12] appearing in NLO QCD calculations. In the last few years, several research groups have been working on extensions of these methods to NNLO [13,14,15,16,17], and, recently, the NNLO calculation for e + e − → 3 jets wa...