An ordered analysis of heavy flavour production in deep inelastic scattering

At low Q2, charm production in deep-inelastic scattering is adequately described by assuming generation in electroweak boson-light parton scattering (dominantly boson-gluon fusion) which naturally incorporates the correct threshold behaviour. At high Q2 this description is inadequate, since it does not sum logs in Q2/mc2, and is replaced by the treatment of the charm quark as a light parton. We show how the problem of going from one description to the other can be solved in a satisfactory manner to all orders. The key ingredient is the constraint of matching the evolution of the physical structure function F2 order by order in αs(Q2) in addition to the matching of the value of F2 itself. This leads to new expressions for the coefficient functions associated with the charm parton which are unique in incorporating both the correct threshold and asymptotic behaviours at each order in perturbation theory. The use of these improved coefficients lead to an improvement in global fits and an excellent description of the observed F2,charm. (author)