SCHEME AND SCALE DEPENDENCE OF CHARM PRODUCTION IN NEUTRINO SCATTERING

We discuss some theoretical uncertainties in the calculation of the cr oss section for charm production in charged current deep inelastic neu trino scattering related to ambiguities in the treatment of terms whic h are singular in the limit of a vanishing charm mass. In particular w e compare the so-called variable flavour scheme where these terms are absorbed in the parton distribution functions containing the charm as an active flavour, with the so-called fixed flavour scheme with no cha rm mass subtraction where the charm appears only in the final state of fixed-order scattering matrix elements. Using available parametrizati ons of parton distribution functions we find that the two schemes lead to largely differing results for separate structure functions whereas the differences cancel to a large extent in the total cross section i n that kinematical region which has been measured so far.