Seminare de DPNC ================ Mercredi, 26 novembre, 1997 17.00 - Auditoire Stuckelberg Universite de Geneve Departement de physique nucleaire et corpusculaire 24, quai Ernest-Ansermet 1211 Geneva 4 Tel. 022 702 6273 Fax. 022 781 2192 ****************************************************************************** Sujet: Soft Interation at HERA Par: Prof. Ralph Eichler, ETHZ Resume: Recent results on hard diffraction at HERA and the Tevatron are presented. The diffractive structure function is measured for the first time and an interpretation in terms of parton densities in the diffractively exchanged object is given. Charged particle multiplicities in diffraction and differences in multiplicity in quark and gluon jets measured at LEP are discussed. Leading particle effects show some unexplained features.