Power corrections to event shapes and factorization

We study power corrections to the differential thrust, heavy mass and related event shape distributions in e⁺e^- annihilation, whose values, e, are proportional to jet masses in the two-jet limit, e → 0. The factorization properties of these differential distributions imply that they may be written as convolutions of non-perturbative "shape" functions, describing the emission of soft quanta by the jets, and resummed perturbative cross sections. The infrared shape functions are different for different event shapes, and depend on a factorization scale, but are independent of the center-of-mass energy Q. They organize all power corrections of the form 1/(eQ)ⁿ, for arbitrary n, and carry information on a class of universal matrix elements of the energy-momentum tensor in QCD, directly related to the energy-energy correlations.