Power corrections to event shapes and factorization

We study power corrections to the differential thrust, heavy mass and relat ed event shape distributions in e(+)e(-) annihilation, whose values, e, are proportional to jet masses in the two-jet limit, e --> 0. The factorizatio n properties of these differential distributions imply that they may be wri tten as convolutions of non-perturbative "shape" functions, describing the emission of soft quanta by the jets, and resummed perturbative cross sectio ns. The infrared shape functions are different for different event shapes, and depend on a factorization scale, but are independent of the center-of-m ass energy Q. They organize all power corrections of the form 1/(eQ)(n), fo r arbitrary n, and carry information on a class of universal matrix element s of the energy-momentum tensor in QCD, directly related to the energy-ener gy correlations. (C) 1999 Elsevier Science B.V. All rights reserved.