The forward-jet cross section in deep inelastic e(+)p scattering has been m
easured 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 transver
se 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 perturbati
ve 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 tes
t. The measured cross section is compared to the predictions of a next-to-l
eading order pQCD calculation as well as to various leading-order Monte Car
lo models. Whereas the predictions of all models agree with the measured cr
oss section in the region of small E-T,jet(2)/Q(2), only one model, which i
ncludes a resolved photon component, describes the data over the whole kine
matic range. (C) 2000 Elsevier Science B.V. All rights reserved.