Measurement of dijet cross sections with leading neutrons in photoproduction at HERA

An analysis is presented of dijets in photoproduction at the ep collider HERA where a leading neutron with an energy En>400 GeV and angle θn<0.8 mrad with respect to the proton direction is detected. The average photon-proton center-of-mass energy is about 200 GeV. Mechanism of leading neutron production is studied. The differential cross sections are measured as function of jet transverse energy and pseudorapidity, the fraction of the photon momenta entering the hard scattering, xγ, and xπ, interpreted as the fraction of pion momenta in a model where the interaction proceeds via exchange of a pion. The Monte Carlo predictions based on standard photoproduction processes and those based on the one-pion-exchange model, using different parameterizations for the pion structure function, are compared to the measurements.