AVERAGE NUMBER OF JETS IN E+E- ANNIHILATION

Using the recently introduced "k (perpendicular-to)" jet clustering algorithm, we are able to compute the average number of hadronic jets produced in e+e- annihilation, as a function of both the centre-of-mass energy and the jet resolution parameter y(cut). For large values of y(cut) we give complete numerical results to order alpha(s)2, using the results of Bethke et al. on multi-jet fractions to this order. For small values, we give the results of resumming leading and next-to-leading logarithms of y(cut) to all orders in QCD perturbation theory. Our predictions should be useful both for determining alpha(s) and for studying the transition from the perturbative to the hadronization regime at very small y(cut).