The dependence of dijet production on photon virtuality in ep collisions at HERA
The dependence of dijet production on the virtuality of the exchanged photon, Q 2, has been studied by measuring dijet cross sections in the range with the ZEUS detector at HERA using an integrated luminosity of 38.6 pb-1. Dijet cross sections were measured for jets with transverse energy and 6.5 GeV and pseudorapidities in the photon-proton centre-of-mass frame in the range . The variable , a measure of the photon momentum entering the hard process, was used to enhance the sensitivity of the measurement to the photon structure. The Q 2 dependence of the ratio of low- to high- events was measured. Next-to-leading-order QCD predictions were found to generally underestimate the low- contribution relative to that at high . Monte Carlo models based on leading-logarithmic parton-showers, using a partonic structure for the photon which falls smoothly with increasing Q 2, provide a qualitative description of the data.
© Springer-Verlag, 2004