Energy flow, event shapes, charm and the structure of the pomeron

Measurements are presented of the system X of the hadronic final state produced in deep-inelastic scattering positron-proton diffractive scattering (e(+)p --> eXY) using data collected by the H1 and ZEUS experiments at HERA. Shown are the hadronic energy flow and charged particle spectra in the rest frame of the system X. Also presented is the average value of thrust [T] as a function of 1/M-x, where Mr is the invariant mass of the system X and the thrust p(T). Also shown is the average sphericity (S) as a function of Mr and the average transverse momentum squared with respect to the sphericity axis [p(T)*(2)], as a function of M-x. The inclusive open charm cross section is also presented. The data are shown to be consistent with a picture in which the partonic structure of the diffractive exchange (P) is dominated by gluons, and cannot be described if the P is composed primarily of quarks.