Elsevier, Physics Letters B, 1-2(474), p. 223-233, 2000
DOI: 10.1016/s0370-2693(99)01478-1
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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, E2T,jet, and Q2 in the kinematic ranges 10−2<E2T,jet/Q2<102 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(E2T,jet/Q2) 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 E2T,jet/Q2, only one model, which includes a resolved photon component, describes the data over the whole kinematic range.