Power Corrections to Event Shape Distributions

TL;DR

Dokshitzer and Webber address power-suppressed corrections to e+e- event shape distributions by extending an infrared-regular effective coupling α_eff to the full distributions. They find that, for thrust, the leading non-perturbative effect is a simple 1/Q shift of the distribution, implemented within a log-R matched resummed perturbative framework and constrained by low-scale moments ᾱ_0 and Λ_MSbar. Through fits to data across a broad energy range, they obtain consistent parameter values and an excellent description of the thrust spectra, linking the results to the dispersive approach. The work also discusses extensions to other jet shapes and the role of large-angle soft radiation in determining the magnitude of power corrections.

Abstract

We estimate the effects of non-perturbative physics on the differential distributions of infrared- and collinear-safe $e^+e^-$ event shape variables, by extending the notion of an infrared-regular effective strong coupling, which accounts for the non-perturbative corrections to the mean values of several shape variables, to their distributions. This leads to $1/Q$ power corrections over a range of values of the shape variables considered, where $Q$ is the centre-of-mass energy. In the case of the thrust variable, the leading correction is simply a shift of the distribution, by an amount proportional to $1/Q$. We show that this gives an excellent description of the data throughout a wide range of $T$ and $Q$.

Figures (2)

• Figure 1: Data on the thrust distribution at various energies, and the prediction (\ref{['Tshift']}) for $\Lambda^{(5)}_{\overline{\hbox{\tiny MS}}} = 0.235$ GeV, $\bar{\alpha}_0 = 0.46$. The twelve data sets are as listed in Table 1 (from top to bottom, multiplied by the factors indicated).
• Figure 2: Best fit values and 95% confidence region for the two fitted parameters. Solid/dashed ellipses: including/excluding 14 GeV data.