Three-jet production in deep inelastic $ep$ scattering and photoproduction was investigated with the ZEUS detector at HERA using an integrated luminosity of up to $127{\mathrm{pb}}^{-1}$. Measurements of differential cross sections are presented as functions of angular correlations between the three jets in the final state and the proton-beam direction. These correlations provide a stringent test of perturbative QCD and show sensitivity to the contributions from different color configurations. Fixed-order perturbative calculations assuming the values of the color factors $C_F$, $C_A$, and $T_F$ as derived from a variety of gauge groups were compared to the measurements to study the underlying gauge group symmetry. The measured angular correlations in the deep inelastic $ep$ scattering and photoproduction regimes are consistent with the admixture of color configurations as predicted by SU(3) and disfavour other symmetry groups, such as $\mathrm{SU}(N)$ in the limit of large $N$.

• Received 30 November 2011

DOI:https://doi.org/10.1103/PhysRevD.85.052008