https://doi.org/10.1140/epjc/s2004-01885-2
experimental physics
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
