Consistent Treatment of Charm Evolution in Deep Inelastic Scattering

Abstract

We present a formulation which allows heavy quark (c, b, ...) mass effects to be explicitly incorporated in both the coefficient functions and the splitting functions in the parton evolution equations. We obtain a consistent procedure for evolution through the threshold regions for c anti-c and b anti-b production in deep inelastic scattering, which allows the prediction of the charm and bottom quark densities. We use the new formulation to perform a next-to-leading order global parton analysis of deep inelastic and related hard scattering data. We find that the optimum fit has alpha_S(M_Z^2) = 0.118. We give predictions for the charm components of the proton structure functions F_2 and F_L as functions of x and Q^2 and, in particular, find that F_2^c is in good agreement with the existing measurements. We examine the Q^2 range of validity of the photon-gluon fusion model for c anti-c electroproduction. We emphasize the value of a precision measurement of the charm component F_2^c at HERA.