A precise determination of alpha_s from LEP thrust data using effective field theory

TL;DR

This paper uses effective field theory to calculate the thrust distribution in electron-positron collisions with high precision, enabling a very accurate determination of the strong coupling constant alpha_s from LEP data.

Contribution

It provides a next-to-next-to-next-to-leading logarithmic resummation of thrust, improving precision over previous methods and enabling a highly accurate alpha_s measurement.

Findings

Alpha_s(m_Z)= 0.1172 with detailed uncertainties

Resummed distribution closely matches fixed-order near the endpoint

Achieves one of the most precise alpha_s extractions to date

Abstract

Starting from a factorization theorem in Soft-Collinear Effective Theory, the thrust distribution in e+e- collisions is calculated including resummation of the next-to-next-to-next-to leading logarithms. This is a significant improvement over previous calculations which were only valid to next-to-leading logarithmic order. The fixed-order expansion of the resummed result approaches the exact fixed-order distribution towards the kinematic endpoint. This close agreement provides a verification of both the effective field theory expression and recently completed next-to-next-to-leading fixed order event shapes. The resummed distribution is then matched to fixed order, resulting in a distribution valid over a large range of thrust. A fit to ALEPH and OPAL data from LEP 1 and LEP 2 produces alpha_s(m_Z)= 0.1172 +/- 0.0010 +/- 0.0008 +/-0.0012 +/- 0.0012, where the uncertainties are respectively statistical, systematic, hadronic, and perturbative. This is one of the world's most precise extractions of alpha_s to date.