Measurement of the inclusive di-jet cross section in photoproduction and determination of an effective parton distribution in the photon

The double- differential inclusivedi-jet cross section in photoproduction processes is measured with the H1 detector at HERA. The cross section is determined as a function of the average transverse jet energyETjets for ranges of the fractional energyξγjets of the partonfrom the photon side. An effective leading order partondistribution in the photon is determined at large partonfractional energies for scale between 80 logarithmic scaledependence that is predicted by perturbative QCD.