Power Corrections in Deep Inelastic Event Shape Variables

Results are presented for the leading power-suppressed (1/Q) contributions to shape variables in deep inelastic lepton scattering. These are then combined with available leading order perturbative estimates. INTRODUCTION The increasing quantity of data from HERA has given a great boost to the testing of QCD via determinations of the strong coupling constant and the possibility of observing, over a wide kinematic range, its running behaviour. However in any comparison between theory and experimental data proper account has to be taken of the non-perturbative behaviour inherent in any observable QCD process. While event shape variables are considered useful observables for αs determinations they can suffer from significant power suppressed effects which are non-perturbative in origin. These 1/Q corrections have already been calculated for a number of ee event shapes [1] and similar results are obtained here for DIS. To make the analogy with ee shape variables clearer it proves useful to work in the Breit frame and to define current jet event shapes as done in the next section. The dispersive approach [2] is used to estimate the power corrections, which is equivalent to a calculation of the leading renormalon ambiguity. EVENT SHAPE VARIABLES One can define several infrared safe quantities that characterize the shape of the event in the current hemisphere Hc of the Breit frame. Perturbative results are available in [3]. The event shapes considered below are the thrust, the jet 1) Talk given at the 5th International Workshop on Deep Inelastic Scattering, Chicago, April 1997. mass, the jet broadening and the C parameter with the following definitions in the above order where ~n denotes a unit 3-vector along the current direction and the summation index a runs over only those partons that are in the current hemisphere.