NNLO moments of event shapes in e+e- annihilation

Abstract

We compute the next-to-next-to-leading order (NNLO) QCD corrections to the first five moments of six event shape variables related to three-particle final states in electron-positron annihilation; the thrust, the heavy jet mass, the C-parameter, the wide and total jet broadenings and the three-to-two-jet transition parameter in the Durham algorithm Y3. The NNLO corrections to the first moment are moderate for all event shapes, while the renormalisation scale dependence of the theoretical prediction is substantially reduced compared to the previously existing NLO results. From a comparison with data from JADE and OPAL, we observe that the energy dependence of the moments of the wide jet broadening and Y3 can be largely explained without any non-perturbative power corrections, while the other observables exhibit a clear need for power-like contributions at low centre-of-mass energy. © 2009 SISSA.