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

The total hadronic cross-section σγγ(W) for the interaction of real photons, γγ→ hadrons, is measured for γγ centre-of-mass energies 10≤W≤110 GeV. The cross-section is extracted from a measurement of the process e+e-→e+e-γ*γ*→e+e-+ hadrons, using a luminosity function for the photon flux together with form factors for extrapolating to real photons (Q2=0 GeV2). The data were taken with the OPAL detector at LEP at e+e- centre-of-mass energies √(s)ee=161, 172 and 183 GeV. The cross-section σγγ(W) is compared with Regge factorisation and with the energy dependence observed in γp and pp interactions. The data are also compared to models which predict a faster rise of σγγ(W) compared to γp and pp interactions due to additional hard γγ interactions not present in hadronic collisions. (orig.)