Universality of non-leading logarithmic contributions in transverse-momentum distributions

We consider the resummation of the logarithmic contributions to the region of small transverse momenta in the distributions of high-mass systems (lept on pairs, vector bosons, Higgs particles,...) produced in hadron collisions . We point out that the resummation formulae that are usually used to compu te the distributions in perturbative QCD involve process-dependent form fac tors and coefficient functions. We present a new universal form of the resu mmed distribution, in which the dependence on the process is embodied in a single perturbative factor. The new form simplifies the calculation of non- leading logarithms at higher perturbative orders. It can also be useful to systematically implement process-independent non-perturbative effects in tr ansverse-momentum distributions. We also comment on the dependence of these distributions on the factorization and renormalization scales. (C) 2001 El sevier Science B.V. All rights reserved.