  We consider higher-order QCD corrections to the production of colourless
high-mass 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.
