QCD in the Precision Era

Abstract

[EN] This thesis presents a precision determination of the strong coupling as(mZ) using event-shape measurements from electron{positron annihilation at LEP. Event shapes provide infrared-safe probes of QCD radiation that are sensitive to both perturbative dynamics and nonperturbative effects, making them powerful observables for extracting "as" in a clean experimental environment. The analyses presented in this work exploit recent theoretical advances that enable a consistent description of event-shape distributions across multiple kinematic regimes. The primary focus is on the thrust and heavy jet mass observables. In the dijet limit, the corresponding distributions are computed using factorization theorems that separate hard, collinear, and soft dynamics, combined with all-order resummation of large logarithms to next-to-next-to-next-to-leading logarithmic (N3LL0) accuracy and matching to xed-order at O(a3 s). Nonperturbative effects are incorporated through operator-based power corrections, including renormalon subtractions that improve perturbative convergence. For the heavy jet mass, additional resummation is performed near the Sudakov shoulder associated with symmetric three-jet con gurations. In addition to the above, a large- 0 analysis is performed, where the leading ambiguity of SCET-II type observables is extracted. This enables one to obtain the leading non-perturbative correction to the cross section prediction for, among others, Broadening and the dijet transverse-momentum decorrelation. E ects on the cross sections are analysed.