A measurement of the di-jet cross-sections in two photon physics at LEP 2

This thesis presents a study of di-jet production in untagged two photon events in the ALEPH detector at LEP with sq root s=183 GeV. A low background sample of 145146 untagged gamma gamma events is obtained and from this 2346 di-jet events are found. A clustering algorithm, KTCLUS, is used to reconstruct the jet momenta. The data is corrected back to hadron level using the PHOJET Monte Carlo and this sample is compared with two independent NLO QCD calculations. Good agreement is seen except at the lowest jet P sub T , where the calculations overshoot the data; however, it should be noted that perturbative QCD is less reliable at low P sub T.