k-factorization and impact factors at next-to-leading level

We further analyse, at next-to-leading log s level, the form of k-factoriza tion and the definition of impact factors previously proposed by one of us, and we generalize them to the case of hard colourless probes. We then calc ulate the finite one-loop corrections to quark and gluon impact factors and we find them universal, and given by the same K factor which occurs in the soft timelike splitting functions. (C) 1999 Elsevier Science B.V.