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

Understand

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.