Transverse momentum distribution of partons in QCD

The renormalization group approach is applied to the study of transverse momentum distribution of partons in QCD. We generalize the method of Altarelli and Parisi to obtain a formula for the mean squared average transverse momentum as a function of Q² and x, the virtual photon mass squared and the longitudinal momentum fraction of the parton. For large Q², it decreases with x in addition to the expected increase with Q². This x-dependence reduces substantially the transverse momentum of massive μ-pairs produced by hadronic collisions from its linear dependence on $\text{(}\text{Q}{}^2\text{ln}\text{Q}{}^2\text{)}\text{1}\text{2}$.