Novel QCD Effects from Initial and Final State Interactions

TL;DR

This paper discusses how initial and final state interactions, involving gluon exchanges, significantly impact QCD hard-scattering processes, leading to observable phenomena like single-spin asymmetries and diffractive scattering, and challenge traditional factorization assumptions.

Contribution

It reveals the profound effects of initial and final state interactions in QCD reactions, highlighting their role in phenomena not accounted for in the conventional parton model.

Findings

Initial and final state interactions cause single-spin asymmetries.

Diffractive deep inelastic scattering leads to nuclear shadowing.

Factorization-breaking effects are significant in hard hadron reactions.

Abstract

Initial-state and final-state interactions, which are conventionally neglected in the parton model, have a profound effect in QCD hard-scattering reactions. These effects, which arise from gluon exchange between the active and spectator quarks, cause leading-twist single-spin asymmetries, diffractive deep inelastic scattering, diffractive hard hadronic reactions, and the breakdown of the Lam-Tung relation in Drell-Yan reactions. Diffractive deep inelastic scattering also leads to nuclear shadowing and non-universal antishadowing of nuclear structure functions through multiple scattering reactions in the nuclear target. Factorization-breaking effects are particularly important for hard hadron interactions since both initial-state and final-state interactions appear. Related factorization breaking effects can also appear in exclusive electroproduction reactions and in deeply virtual Compton scattering. None of the effects of initial-state and final-state interactions are incorporated in the light-front wavefunctions of the target hadron computed in isolation.