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

The total hadronic cross-section sigma gamma gamma(W) for the interaction of real photons, gamma gamma --> hadrons, is measured for gamma gamma centre-of-mass energies 10 less than or equal to W less than or equal to 110 GeV. The cross-section is extracted from a measurement of the process e(+)e(-) --> e(+)e(-) gamma*gamma* --> e(+)e(-) + hadrons, using a luminosity function for the photon flux together with form factors for extrapolating to real photons (Q(2) = 0 GeV2). The data, were taken with the OPAL detector at LEP at e(+)e(-) centre-of-mass energies root s(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 yp 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.