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.