On power corrections to the event shape distributions in QCD

We study power corrections to the differential thrust, heavy jet mass and C-parameter distributions in the two-jet kinematical region. We argue that away from the end-point region, e >> Lambda (QCD)/Q, the leading 1/Q-power corrections are parameterized by a single non-perturbative scale while for e similar to Lambda (QCD)/Q one encounters a novel regime in which power corrections of the form 1/(Qe)(n) have to be taken into account for arbitrary n. These non-perturbative corrections can be resummed and factor out into a universal non-perturbative distribution, the shape function, and the differential event shape distributions are given by convolution of the shape function with perturbative cross-sections. Choosing a simple ansatz for the shape function we demonstrate a good agreement of the obtained QCD predictions for the distributions and their lowest moments with the existing data over a wide energy interval.