Charm Production in Deep Inelastic Scattering

Charm quarks are produced copiously in deep inelastic scattering (DIS) at HERA. At sufficiently high photon virtualities, Q, the production of charm quarks constitutes up to 30% of the total cross section [1,2]. Previous measurements of D∗ cross sections [1,2,3,4] indicate that the production of charm quarks in DIS in the range 1 < Q < 600 GeV is consistent with QCD calculations in which charm is produced through the boson-gluon-fusion mechanism. This implies that the charm cross section is directly sensitive to the gluon density in the proton. In this paper, measurements of the D∗ cross section [5] are presented with improved precision and in a kinematic region extending to higher Q than the previous ZEUS results [1]. The cross sections are compared to a next-to-leading-order (NLO) QCD calculation using various parton density functions (PDFs) in the proton. In particular, the data are compared to calculations using the recent ZEUS NLO fit [6], in which the parton densities in the proton are parametrised by performing fits to inclusive DIS measurements from ZEUS and fixed-target experiments. The cross-section measurements are used to extract the charm contribution, F cc̄ 2 , to the proton structure function, F2.