Measurement of the inclusive di-jet cross section in photoproduction and determination of an effective parton distribution in the photon
The double-differential inclusive di-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 energy & E_T^jets& for ranges of the fractional energy & x_\gamma^jets& of the parton from the photon side. An effective leading order parton distribution in the photon is determined at large parton fractional energies for scales between & 80 < p_T^2 < 1250 GeV^2$. The measurement is compatible with the logarithmic scale dependence that is predicted by perturbative QCD.