Factorization and its Breaking in Dijet Single Transverse Spin Asymmetries in $pp$ Collisions

TL;DR

This paper investigates the validity of TMD factorization in single transverse spin asymmetries for dijet production in proton-proton collisions, revealing its breakdown at NLL accuracy due to soft gluon radiation effects.

Contribution

It demonstrates the breakdown of TMD factorization at NLL accuracy in dijet asymmetries caused by soft gluon radiation effects, providing leading logarithmic predictions for RHIC.

Findings

TMD factorization holds at leading logarithmic level.

Soft gluon radiation causes factorization breaking at NLL.

Predictions for RHIC dijet asymmetries based on Sivers functions.

Abstract

We study factorization in single transverse spin asymmetries for dijet production in proton-proton collisions, by considering soft gluon radiation at one-loop order. We show that the associated transverse momentum dependent (TMD) factorization is valid at the leading logarithmic level. At next-to-leading-logarithmic (NLL) accuracy, however, we find that soft gluon radiation generates terms in the single transverse spin dependent cross section that differ from those known for the unpolarized case. As a consequence, these terms cannot be organized in terms of a spin independent soft factor in the factorization formula. We present leading logarithmic predictions for the single transverse spin dijet asymmetry for $pp$ collisions at RHIC, based on quark Sivers functions constrained by semi-inclusive deep inelastic scattering data. We hope that our results will contribute to a better understanding of TMD factorization breaking effects at NLL accuracy and beyond.