Effective Field Theory Factorization for Diffraction

TL;DR

This paper develops a comprehensive effective field theory framework for understanding both coherent and incoherent diffraction in electron-proton scattering, addressing small-x Regge dynamics and Pomeron exchange from first principles.

Contribution

It introduces a novel factorization formula using soft collinear effective theory that extends beyond known models to include quasi-diffraction and spin-dependent effects.

Findings

Identifies four leading-power diffractive structure functions for unpolarized scattering.

Provides model-independent predictions for ratios of structure functions in perturbative regimes.

Predicts six spin-dependent structure functions relevant for polarized diffraction studies.

Abstract

We derive a factorization formula for coherent and incoherent $ep$ diffraction using the soft collinear effective theory, utilizing multiple power expansion parameters to handle different kinematic regions. This goes beyond the known hard-collinear diffractive factorization to address the small-$x$ Regge dynamics and Pomeron exchange from first principles. The effective field theory analysis also uncovers and factorizes an important irreducible incoherent background generated by color-nonsinglet exchange, dubbed "quasi-diffraction", for which we calculate the associated Sudakov suppression. For unpolarized scattering we show that there are four diffractive structure functions at leading power, and point out the importance of studying $F_{3,4}^D$ through asymmetries, in addition to $F_{2,L}^D$. For the quasi-diffractive background, we make model independent predictions for ratios of the corresponding structure functions in a perturbative kinematic region. Our analysis also makes predictions for six leading-power spin-dependent structure functions. Finally, we provide connections to diffractive parton distributions, and assess the Ingelman-Schlein model. Our work lays a path for further QCD-based studies of diffraction.