Event isotropy in perturbative QCD

Abstract

It has recently been proposed that collider events can be equipped with a metric, the Energy Mover's Distance (EMD), which allows one to rephrase multiple aspects of collider physics in a geometric language. Further, the EMD can be exploited to define new observables. In this context, event isotropy quantifies the resemblance of an event to a uniform energy distribution. We present the first theoretical study of event isotropy within the framework of perturbative QCD. In particular, we first obtain the isotropy distribution in $e^+e^-$ collisions semi-analytically at $O(α_s)$ (leading-order) and numerically at $O(α_s^2)$ (next-to-leading order, NLO). Furthermore, we obtain all-order theoretical predictions by resumming the contributions of soft and collinear emissions, at next-to-leading logarithmic (NLL) accuracy. By matching resummed and fixed-order predictions we reach NLL+NLO accuracy.