Properties of hadronic final states in diffractive deep inelastic scattering at HERA

Characteristics of the hadronic final state of diffractive deep inelastic scattering events ep→eXp were studied in the kinematic range 4<M X35GeV, 4<Q2<150 GeV2, 70< W < 250 GeV, and 0.0003<xp <0.03 with the ZEUS detector at the DESY ep collider HERA using an integrated luminosity of 13.8 pb-1. The events were tagged by identifying the diffractively scattered proton using the leading proton spectrometer. The properties of the hadronic final state X were studied in its center-of-mass frame using thrust, thrust angle, sphericity, energy flow, transverse energy flow, and "seagull" distributions. As the invariant mass of the system increases, the final state becomes more collimated, more aligned, and more asymmetric in the average transverse momentum with respect to the direction of the virtual photon. Comparisons of the properties of the hadronic final state with predictions from various Monte Carlo model generators suggest that the final state is dominated by qq̄g states at the parton level.