e + e − angularity distributions at NNLL′ accuracy

Abstract

We present predictions for the e+e− event shape angularities at NNLL′ resummed and O(αs2) matched accuracy and compare them to LEP data at center-of-mass energies Q = 91.2 GeV and Q = 197 GeV. We perform the resummation within the framework of Soft-Collinear Effective Theory, and make use of recent results for the two-loop angularity soft function. We determine the remaining NNLL′ and O(αs2) ingredients from a fit to the EVENT2 generator, and implement a shape function with a renormalon-free gap parameter to model non-perturbative effects. Using values of the strong coupling αs(mZ) and the universal non-perturbative shift parameter Ω1 that are consistent with those obtained in previous fits to the thrust and C-parameter distributions, we find excellent agreement between our predictions and the LEP data for all angularities with a ∈ [−1, 0.5]. This provides a robust test of the predictions of QCD, factorization, and the universal scaling of the non-perturbative shift across different angularities. Promisingly, our results indicate that current degeneracies in the {αs(mZ), Ω1} parameter space could be alleviated upon fitting these parameters to experimental data for the angularity distributions.