The thrust and heavy-jet mass distributions in the two-jet region

Dressed Gluon Exponentiation (DGE) is used to calculate the thrust and the heavy-jet mass distributions in e ⁺ e ^- annihilation in the two-jet region. We perform a detailed analysis of power corrections, taking care of the effect of hadron masses on the measured observables. In DGE the Sudakov exponent is calculated in a renormalization-scale invariant way using renormalon resummation. Neglecting the correlation between the hemispheres in the two-jet region, we express the thrust and the heavy-jet mass distributions in terms of the single-jet mass distribution. This leads to a simple description of the hadronization corrections to both distributions in terms of a single shape function, whose general properties are deduced from renormalon ambiguities. Matching the resummed result with the available next-to-leading order calculation, we get a good description of the thrust distribution in a wide range, whereas the description of the heavy-jet mass distribution, which is more sensitive to the approximation of the phase space, is restricted to the range ρ _H < 1/6. This significantly limits the possibility to determine α _s from this observable. However, fixing α _s by the thrust analysis, we show that the power corrections for the two observables are in good agreement.