Diffractive charm and dijets production at H1

Abstract

The factorization of diffractive ep cross sections into a (perturbatively accessible) matrix e lement and a diffractive structure function was proven for the case of DIS by Collins in 1998. Diffractive dijet and open charm production provide a valuable probe to testing factorization and characterize possible mechanisms of factorization breaking. Measurements of diffractive dijet and open charm production in DIS and photoproduction made with the H1 detector at the HERA accelerator are presented. Diffractive events were identified by a rapidity gap selection. The resulting differential cross sections are compared to QCD calculations in NLO, based on structure functions extracted from inclusive diffraction. The cross section measurements of diffractive open charm production in DIS and photoproduction agree well with the NLO QCD predictions, supporting factorization. The prediction also describes the dijet data rather well at low momentum fractions zIP of the diffractive exchange carried by the gluon, where the gluon density is known well from the observed scaling violations of the inclusive diffractive data. A new set of parton densities is obtained b y the simultaneous fit to the inclusive diffractive data of previous measurements and the new dijet results. The diffractive dijet cross section in photoproduction is significantly suppressed wit h respect to the expectations from QCD factorization.