Total hadronic cross-section of photon-photon interactions at LEP

Abstract.

The total hadronic cross-section $\sigma_{\gamma \gamma }(W)$ for the interaction of real photons, $\gamma\gamma\rightarrow$ hadrons, is measured for $\gamma\gamma$ centre-of-mass energies $10\le W \le 110$ GeV. The cross-section is extracted from a measurement of the process ${\rm e}^+{\rm e}^-\rightarrow{\rm e}^+{\rm e}^-\gamma^*\gamma^*\rightarrow{\rm e}^+{\rm e}^-+$ hadrons, using a luminosity function for the photon flux together with form factors for extrapolating to real photons ($Q^2=0$ GeV$^2$). The data were taken with the OPAL detector at LEP at ${\rm e}^+{\rm e}^-$ centre-of-mass energies $\sqrt{s}_{\rm ee}=161$, 172$ and 183 GeV. The cross-section $\sigma_{\gamma\gamma}(W)$ is compared with Regge factorisation and with the energy dependence observed in $\gamma$p and pp interactions. The data are also compared to models which predict a faster rise of $\sigma_{\gamma\gamma}(W)$ compared to $\gamma$p and pp interactions due to additional hard $\gamma\gamma$ interactions not present in hadronic collisions.