Hadronic cross-sections in gamma gamma processes and the next linear   collider
  In this note we address the issue of theoretical estimates of the hadronic cross-sections for \gamgam processes. We compare the predictions of the minijet model with data as well as other models, highlighting the band of uncertainties in the theoretical predictions as well as those in the final values of the $\sigma (\gamgam \go {\rm hadrons})$ extracted from the data. We find that the rise of $\sigma_{\gamma \gamma}^{\rm tot}$ with energy shown in the latest \gamgam data is in tune with the faster rise expected in the Eikonal Minijet Models (EMM). We present an estimate of the accuracy with which this cross-section needs to be measured, in order to distinguish between the different theoretical models which try to `explain ' the rise of total cross-sections with energy. We find that the precision of measurement required to distinguish the EMM type models from the proton-like models, for $300 < \sqrt{s}_{\gamgam} < 500$ GeV, is $\lsim 20 %$, whereas to distinguish between various proton-like models or among the different parametrizations of the EMM, a precision of $\lsim 8-9 %$ or $\lsim 6-7%$ respectively, is required. We also comment briefly on the implications of these predictions for hadronic backgrounds at the next linear collider (NLC) to be run in the \gamgam mode or \eplem mode. 
Rohini M. Godbole, G. Pancheri