The Q2 dependence of dijet cross sections in γp interactions at HERA

The dependence of the photon structure on the photon virtuality, Q2, is studied by measuring the reaction e+p→e++jet+jet+X at photon-proton centre-of-mass energies 1345.5 GeV in the final state. The dijet cross section has been measured as a function of the fractional momentum of the photon participating in the hard process, xγOBS. The ratio of the dijet cross section with xγOBS<0.75 to that with xγOBS>0.75 decreases as Q2 increases. The data are compared with the predictions of NLO pQCD and leading-order Monte Carlo programs using various parton distribution functions of the photon. The measurements can be interpreted in terms of a resolved photon component that falls with Q2 but remains present at values of Q2 up to 4.5 GeV2. However, none of the models considered gives a good description of the data.