Problems in the resummation of soft-gluon effects in the transverse-momentum distributions of massive vector bosons in hadronic collisions

We consider the resummation of soft-gluon emission in the transverse-moment um distribution of vector mesons in hadronic collisions. We find that the r esummed expression in the impact-parameter formulation has an expansion in alpha(s) with factorially growing terms with oscillating signs. These diver ging terms arise from the small impact-parameter region of integration, and are of a subleading nature. We also obtain a closed expression for the nex t-to-leading logarithm resummation in qT-space, and we study its analytic s tructure. We find in this case that. although no factorially growing terms are present, there are geometrical singularities that severely restrict the range of applicability of the resummation formula, (C) 1999 Elsevier Scien ce B.V.