Truncated moments of parton distributions

We derive evolution equations satisfied by moments of parton distributions when the integration over the Bjorken variable is restricted to a subset (x (0) less than or equal to x less than or equal to 1) of the allowed kinemat ical range 0 less than or equal to x less than or equal to 1. The correspon ding anomalous dimensions turn out to be given by a triangular matrix which couples the N-th truncated moment with all (N + K)-th truncated moments wi th integer K greater than or equal to 0. We show that the series of couplin gs to higher moments is convergent and can be truncated to low orders while retaining excellent accuracy. We give an example of application to the det ermination of alpha(s) from scaling violations. (C) 1999 Published by Elsev ier Science B.V. All rights reserved.