Speaker: John C. Collins (Pennsylvania State University)
Title:
Fully Unintegrated Parton Correlation Functions and Factorization
in Lowest Order Hard Scattering
Abstract:
Motivated by the need to correct the potentially large kinematic
errors in approximations used in the standard formulation of
perturbative QCD, we reformulate deeply inelastic lepton-proton
scattering in terms of gauge invariant, universal parton correlation
functions which depend on all components of parton four-momentum.
Currently, different hard QCD processes are described by very different
perturbative formalisms, each relying on its own set of kinematical
approximations. In this paper we show how to set up formalism that
avoids approximations on final-state momenta, and thus has a very
general domain of applicability. The use of exact kinematics introduces
a number of significant conceptual shifts already at leading order,
and tightly constrains the formalism. We show how to define parton
correlation functions that generalize the concepts of parton density,
fragmentation function, and soft factor. After setting up a general
subtraction formalism, we obtain a factorization theorem. To avoid
complications with Ward identities the full derivation is restricted
to abelian gauge theories; even so the resulting structure is highly
suggestive of a similar treatment for non-abelian gauge theories.