Sea Change

Introduction to GPDs and TMDs

“…1. In the forward limit ∆ = 0, parton correlation functions that are not integrated over any component of k (called "doubly" or "fully unintegrated" distributions) have been discussed in the context of evolution at small x [6] and with the aim of having an exact description of final-state kinematics [7,8]. Under the name of "beam functions", they have also been introduced in soft-collinear effective theory (SCET) for the resummation of large logarithms in observables sensitive to the proton remnants (called "beam jets") [9,10,11].…”