Measurement of dijet cross sections with a leading neutron in photoproduction at HERA

Differential cross sections for the reaction e+p→e++2 jets+n+X in the photoproduction regime (the virtuality of the exchanged photon in the range Q2<4GeV2, and the fraction y of the positron's energy carried by the exchanged photon in the range 0.2 < y < 0.8) have been measured with the ZEUS detector at HERA at a centre-of-mass energy of √(s)=300 GeV, using an integrated luminosity of 6.4 pb-1. Cross sections are given for jet transverse energies ETjet> 6 GeV, neutron energy En>400 GeV, and neutron scattering angle θ<0.8 mrad. We have measured the fraction of all events with two jets (dijet events) which contain a leading neutron in the final state. The predictions of the one-pion-exchange model, describing the ep→enX interac tion through the exchange of a pion, are found to be in reasonable agreement with the measurements presented here; namely, the dijet differential cross section as a function of the jet transverse energies, the jet pseudorapidities, and the fraction of the momentum carried by the pion participating in the production of the dijet system. (orig.)