Measurement of angular correlations in three-jet productionin with ZEUS at HERA

Three-jet production in the deep inelastic scattering and
photoproduction regimes was investigated with the ZEUS detector
at HERA using an integrated luminosity of 127 pb-1. Jets were
identified using the kT cluster algorithm in the longitudinally
invariant inclusive mode. Measurements of differential cross sections
are presented as functions of jet angular correlations between the
three jets in the final state and the proton-beam direction. These
correlations were investigated to separate the contributions
from different color configurations; in particular, angular
correlations sensitive to the presence of a triple-gluon vertex were
analysed. Fixed-order perturbative QCD calculations assuming the values
of the colour factors C_F, C_A and T_F as derived from a variety
of gauge groups are compared to the measurements to study the
underlying gauge group symmetry.