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

A recent experiment at Fermilab with tagged photon beam has extended the total-cross-section measurements ${\sigma }_T\left(\gamma p\right)$ to $E_{\gamma }=180\mathrm{}$ GeV. In an earlier work, we have applied the core-valence quark model, using light quarks only, together with vector-meson dominance to describe ${\sigma }_T\left(\gamma p\right)$ 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 μb in ${\sigma }_T\left(\gamma p\right)$ 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.