Non-perturbative contribution to the thrust distribution in e+e− annihilation

We re-evaluate the non-perturbative contribution to the thrust distribution in e+e−→ hadrons, in the light of the latest experimental data and the recent NNLO perturbative calculation of this quantity. By extending the calculation to NNLO+NLL accuracy, we perform the most detailed study to date of the effects of non-perturbative physics on this observable. In particular, we investigate how well a model based on a low-scale QCD effective coupling can account for such effects. We find that the difference between the improved perturbative distribution and the experimental data is consistent with a 1/Q-dependent non-perturbative shift in the distribution, as predicted by the effective coupling model. Best fit values of αs(91.2 GeV)=0.1164−0.0026+0.0028 and α0(2 GeV)=0.59±0.03 are obtained with χ2/d.o.f.=1.09. This is consistent with NLO+NLL results but the quality of fit is improved. The agreement in α0 is non-trivial because a part of the 1/Q-dependent contribution (the infrared renormalon) is included in the NNLO perturbative correction.