Sudakov resummation in QCD

Sudakov Resummation in QCD Paolo Bolzoni In this thesis, we have analyzed and generalized the renormalization group approach to the resummation of large logarithms in the perturbative expansion due to soft and collinear multiparton emissions. In particular, we have presented a generalization to prompt photon production of the approach to Sudakov resummation. It is interesting to see that also with the more intricate two-scale kinematics that characterizes prompt photon production in the soft limit, it remains true that resummation simply follows from general kinematic properties of the phase space. Also, this approach does not require a separate treatment of individual colour structures when more than one colour structure contributes to fixed order results. However, the resummation formulae obtained here turn out to be less predictive than previous results: this depends on the fact that here neither specific factorization properties of the cross section in the soft limit is assumed, nor that soft emission satisfies eikonal-like relations. We have also proved a resumation formula for the Drell-Yan rapidity distributions to all logarithmic accuracy and valid for all values of rapidity. This shows that NLL resummation has an important effects on predictions of differential rapidity cross sections giving an agreement with data that is better than NNLO full calculations. We outline also possible future applications of the renormalization group approach.