NNLO corrections to event shapes in $e^+e^-$ annihilation

TL;DR

This paper calculates NNLO QCD corrections to key event shape variables in electron-positron annihilation, significantly improving the agreement between theory and experiment and enabling more precise measurements of the strong coupling constant.

Contribution

The paper presents the first NNLO QCD corrections for six major event shape variables in $e^+e^-$ annihilation, reducing theoretical uncertainties.

Findings

NNLO corrections are sizeable and vary across observables.

Theoretical predictions better match experimental data in shape and normalization.

Renormalisation scale dependence is significantly reduced at NNLO.

Abstract

We compute the next-to-next-to-leading order (NNLO) QCD corrections to the six most important event shape variables related to three-particle final states in electron-positron annihilation. The corrections are sizeable for all variables, however their magnitude is substantially different for different observables. We observe that the NNLO corrections yield a considerably better agreement between theory and experimental data both in shape and normalisation of the event shape distributions. The renormalisation scale dependence of the theoretical prediction is substantially reduced compared to the previously existing NLO results. Our results will allow a precise determination of the strong coupling constant from event shape data collected at LEP.