Scale breaking at large x-intrinsic charm or higher twist?

Abstract

A hard intrinsic charm component of nucleon, as suggested by Brodsky et al., is first shown to be consistent with the available μN→μμX data, assuming a reasonable threshold factor. Such a hard charm contribution is then included in a QCD analysis of the structure function data at largex(>0.3), where the gluon contribution to the evolution equation can be safely neglected. Whereas a pure QCD fit results in a Λ going down significantly with increasing Q ², inclusion of the hard charm contribution results in a consistent description of all data with a common Λ300-400 MeV. Alternatively a consistent QCD fit to these data can be obtained by including a higher twist contribution, in which case the common Λ has a much smaller value ≃100 MeV.