Azimuthal decorrelations between QCD jets at all orders

TL;DR

The paper tackles the azimuthal decorrelation $\Delta \phi$ between jets as a probe of QCD dynamics, showing that accurate predictions require NLL resummation in the back-to-back region and that the jet recombination scheme crucially determines whether the observable is global or non-global. It develops a $b$-space resummation framework for the global variant, decomposing the radiator into in-jet, out-of-jet, and soft wide-angle components and extending the approach to hadron collisions. The results demonstrate that, in a global recombination scheme, the resummation cures the fixed-order divergence near $\Delta \phi \approx \pi$ and provides a pathway toward matching with fixed order and incorporating non-perturbative effects. The work also analyzes non-global effects in the alternative E-scheme, finding them numerically small in the back-to-back region, thereby reinforcing the observable's practicality for phenomenology.

Abstract

A quantity that promises to reveal important information on perturbative and non-perturbative QCD dynamics is the azimuthal decorrelation between jets in different hard processes. In order to access this information fixed-order NLO predictions need to be supplemented by resummation of logarithmic terms which are large in the region where the jets are nearly back-to-back in azimuth. In the present letter we carry out this resummation to next-to--leading logarithmic accuracy explaining the important role played by the recombination scheme in general resummations for such jet observables.