Measurement of the E^2_(T,jet)/Q^2 dependence of forward-jet production at HERA

The forward-jet cross section in deep inelastic e(+)p scattering has been measured using the ZEUS detector at HERA with an integrated luminosity of 6.36 pb(-1). The jet cross section is presented as a function of jet transverse energy squared, E(T,jet)(2), and Q(2) in the kinematic ranges 10(-2) < E(T,jet)(2)/Q(2) < 10(2) and 2.5.10(-4) < x < 8.0.10(-2). Since the perturbative QCD predictions for this cross section are sensitive to the treatment of the log(E(T,jet)(2)/Q(2)) terms, this measurement provides an important test. The measured cross section is compared to the predictions of a next-to-leading order pQCD calculation as well as to various leading-order Monte Carlo models. Whereas the predictions of all models agree with the measured cross section in the region of small E(T,jet)(2)/Q(2), only one model, which includes a resolved photon component, describes the data over the whole kinematic range.