Electroweak Gauge-Boson Production at Small q_T: Infrared Safety from the Collinear Anomaly

TL;DR

This paper introduces a new effective field theory framework for calculating electroweak gauge-boson production at small transverse momentum, resumming large logarithms and accounting for the collinear anomaly, with applications to collider data.

Contribution

It develops a systematic, novel method using effective field theory to accurately compute small q_T cross sections, including non-perturbative effects and anomaly considerations.

Findings

Resummed cross sections match Tevatron and LHC data.

Identified a non-perturbative scale q_* that stabilizes calculations.

Derived explicit expressions for the q_T=0 cross section intercept.

Abstract

Using methods from effective field theory, we develop a novel, systematic framework for the calculation of the cross sections for electroweak gauge-boson production at small and very small transverse momentum q_T, in which large logarithms of the scale ratio M_V/q_T are resummed to all orders. These cross sections receive logarithmically enhanced corrections from two sources: the running of the hard matching coefficient and the collinear factorization anomaly. The anomaly leads to the dynamical generation of a non-perturbative scale q_* ~ M_V e^{-const/\alpha_s(M_V)}, which protects the processes from receiving large long-distance hadronic contributions. Expanding the cross sections in either \alpha_s or q_T generates strongly divergent series, which must be resummed. As a by-product, we obtain an explicit non-perturbative expression for the intercept of the cross sections at q_T=0, including the normalization and first-order \alpha_s(q_*) correction. We perform a detailed numerical comparison of our predictions with the available data on the transverse-momentum distribution in Z-boson production at the Tevatron and LHC.