Consistent treatment of charm evolution in deep inelastic scattering

Abstract.

We present a formulation which allows heavy quark $(c, b, \ldots)$ 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 $c\overline c$ and $b\overline{b}$ 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 $c\overline c$ electroproduction. We emphasize the value of a precision measurement of the charm component $F_2^c$ at HERA.