Multiplicity Structure of the Hadronic Final State inDi ractive Deep-Inelastic Scattering at HERA H 1 Collaboration

ISSN 0418-9833 Multiplicity Structure of the Hadronic Final State in Di ractive Deep-Inelastic Scattering at HERA H1 Collaboration Abstract The multiplicity structure of the hadronic system X produced in deep-inelastic processes at HERA of the type ep ! eXY , where Y is a hadronic system with mass MY < 1:6 GeV and where the squared momentum transfer at the pY vertex, t, is limited to jtj < 1 GeV2, is studied as a function of the invariant mass MX of the system X. Results are presented on multiplicity distributions and multiplicity moments, rapidity spectra and forward-backward correlations in the centre-ofmass system of X. The data are compared to results in e+e annihilation, xedtarget lepton-nucleon collisions, hadro-produced di ractive nal states and to nondi ractive hadron-hadron collisions. The comparison suggests a production mechanism of virtual photon dissociation which involves a mixture of partonic states and a signi cant gluon content. The data are well described by a model, based on a QCD-Regge analysis of the di ractive structure function, which assumes a large hard gluonic component of the colourless exchange at low Q2. A model with soft colour interactions is also successful.