Charm photoproduction dynamics

Photoproduction of open charm is reviewed, both as a tool for studying the properties of charm particles such as spectroscopy, decays, and lifetimes, and as a testing ground for theoretical calculations of production dynamics. Many characteristics of charm photoproduction are described in terms of the leading order (LO) {alpha}{sub EM}{alpha}{sub S} Photon-Gluon Fusion (PGF) model. The next-to-leading order (NLO) corrections of strength {alpha}{sub EM}{alpha}{sub S}{sup 2} due to radiation of additional gluons are then added. The sensitivities of the NLO calculations on the mass of the charm quark, m{sub c}, and on the choice of the gluon structure function of the nucleon are illustrated for the energy dependence of the cross section for charm photoproduction. These are compared with fixed target data and new HERA data. The single charm particle inclusive distributions in x{sub f} and p{sub {perpendicular}}{sup 2}, along with {sigma}({gamma}N {yields} c{anti c}X) give good estimates of m{sub c} and n{sub g}, the shape parameter for the gluon distribution within the nucleon. As in hadroproduction, some disagreements between prediction and observation begin to appear in trying to simultaneously match the distributions in both p{sub {perpendicular}}{sup 2} for single charm particles and in the {Delta}{Phi} acoplanarity angle between pairs of charm particles. These can be partially remedied by modifying the fragmentation function for c-quarks into charm particles, and by including extra k{sub {perpendicular}}{sup 2} transverse smearing of the gluon distributions within the target nucleon. Initial studies of the relative production between charm particles and anti-particles indicate disagreement with the predictions of the independent string fragmentation model