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Particle and Astro-Particle Physics Seminars
New approach to QCD factorization
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Europe/Zurich
4/3-006 - TH Conference Room (CERN)
Description
Factorization is a fundamental concept suggested in order to apply QCD calculations to description of hadronic reactions. According to this concept, theoretical study of any hadronic process should combine perturbative cal- culations (to calculate partonic sub-processes) with parton distributions (to proceed from the partons to hadrons). The partonic sub-processes are calculated with the use of regular technique developed in the Perturbative QCD (either in fixed orders in the coupling or by using Evolution Equations). In contrast, the parton distributions are introduced purely phenomenologically without any theoretical grounds. There are two kinds of QCD factorization available in the literature: Collinear and KT - factorizations introduced independently of each other.
Considering the forward Compton amplitudes off hadrons and the structure functions of Deep-Inelastic Scattering, we show that both KT- and Collinear factorizations can be obtained by consecutive reductions of a more general factorization which we call Basic factorization. Each of these reduc- tions is an approximation valid under certain assumptions. In particular, the transition to the KT - factorization is possible when the longitudinal momenta of the partons connecting the perturbative and non-perturbative blobs are small compared to their transverse momenta. Then, if the unintegrated par- ton distributions in KT -factorization have one or several maximums in k⊥, KT -factorization can be reduced to Collinear factorization. This feature of the parton distributions can be checked with analysis of experimental data.
As an application of our results, we obtain theoretical restrictions on fits for the parton distributions. First, we predict a general form of fits for parton distributions in KT - factorization. Second, we exclude the use of singular factors x−a (with a > 0) in fits for the initial quark and gluon distributions in both KT - and Collinear factorizations
