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

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 LEP1 and LEP2 produces α s(m Z) = 0.11720.00100.00080.00120.0012, where the uncertainties are respectively statistical, systematic, hadronic, and perturbative. This is one of the world's most precise extractions of α s to date.