Heavy quarks and the measured surplus in the high-energy total photoproduction cross section

Abstract

A recent experiment at Fermilab with tagged photon beam has extended the total-cross-section measurements ${\ensuremath{\sigma}}_{T}(\ensuremath{\gamma}p)$ to ${E}_{\ensuremath{\gamma}}=180$ GeV. In an earlier work, we have applied the core-valence quark model, using light quarks only, together with vector-meson dominance to describe ${\ensuremath{\sigma}}_{T}(\ensuremath{\gamma}p)$ up to 10 GeV. We have now extended our model by including the heavy-quark contribution, and in spite of this addition we find a definiency of 2-5 \ensuremath{\mu}b in ${\ensuremath{\sigma}}_{T}(\ensuremath{\gamma}p)$ in the high-energy region. Calculations within the framework of other models fail to account for the surplus in the experimental data. On extending the model to electroproduction we again encounter normalization difficulties.