Multijet production at low xbj in deep inelastic scattering at HERA

Dijet and trijet production in deep inelastic ep scattering has been measured in the phase space region 10 < Q(2) < 100 GeV2 and 10(-4) < x(Bj) < 10(-2) using an integrated luminosity of 82 pb(-1) collected by the ZEUS experiment. The high statistics have made possible detailed studies of multijet production at low xBj. The dependence of dijet and trijet production on the kinematic variables Q(2) and x(Bj) and on the jet variables E-T,HCM(jet) and eta(jet)(LAB) is well described by perturbative QCD calculations which include NLO corrections. To investigate possible deviations with respect to the collinear factorisation approximation used in the standard pQCD approach, measurements of the correlations between the two jets with highest E-T,HCM(jet) have been made. At low x(Bj), measurements of dijet production with low azimuthal separation are reproduced by the perturbative QCD calculations provided that higher-order terms (O(alpha(3)(s))) are accounted for. Such terms increase the predictions of pQCD calculations by up to one order of magnitude when the two jets with the highest E-T,HCM(jet1,2) are not balanced in transverse momentum. This demonstrates the importance of higher-order corrections in the low-x(Bj) region.