Factorization for Azimuthal Asymmetries in SIDIS at Next-to-Leading Power

TL;DR

This paper derives a rigorous factorization formula for azimuthal asymmetries in SIDIS at next-to-leading power using Soft Collinear Effective Theory, enabling more precise theoretical predictions of hadron structure.

Contribution

It provides the first complete factorization framework for subleading power effects in SIDIS azimuthal asymmetries, including generalized TMD definitions and perturbative corrections.

Findings

Derived a complete factorization formula for subleading power SIDIS effects.

Defined generalized TMDs depending on two longitudinal momentum fractions.

Showed only the leading soft function appears at this order, simplifying calculations.

Abstract

Differential measurements of the semi-inclusive deep inelastic scattering (SIDIS) process with polarized beams provide important information on the three-dimensional structure of hadrons. Among the various observables are azimuthal asymmetries that start at subleading power, and which give access to novel transverse momentum dependent distributions (TMDs). Theoretical predictions for these distributions are currently based on the parton model rather than a rigorous factorization based analysis. Working under the assumption that leading power Glauber interactions do not spoil factorization at this order, we use the Soft Collinear Effective Theory to derive a complete factorization formula for power suppressed hard scattering effects in SIDIS. This yields generalized definitions of the TMDs that depend on two longitudinal momentum fractions (one of them only relevant beyond tree level), and a complete proof that only the same leading power soft function appears and can be absorbed into the TMD distributions at this order. We also show that perturbative corrections can be accounted for with only one new hard coefficient. Factorization formulae are given for all spin dependent structure functions which start at next-to-leading power. Prospects for improved subleading power predictions that include resummation are discussed.