Total Hadronic (γ,p) and (γ,d) Cross Sections from 4 TO 18 GeV

Abstract

Photoabsorption cross sections in hydrogen and deuterium have been measured from 3.7 to 17.9 GeV. The energy dependences are similar to those of strong-interaction total cross sections, as expected from the vector-meson-dominance model. The magnitude of ${\sigma }_T\left(\gamma p\right)$ can be compared with data from $\gamma p\to {\rho }^{0}p$ to determine a $\gamma -p$ coupling constant, $\frac{{{\gamma }_{\rho }}^2}{4\pi }=0.37\mathrm{}\pm 0.03$. This value disagrees with that obtained on the $\rho$ mass shell, and hence there is only qualitative agreement with the vector-meson-dominance model.