Diffractive Dijets in DIS and Photoproduction

Abstract

The factorization of diffractive ep cross sections into a (perturbatively accessible) matrix element and a diffractive structure function was proven for the case of DIS by Collins in 1998. This factorization is not expected to hold for Photoproduction. Diffractive dijet production provides a valuable probe to testing factorization and characterize possible mechanisms of factorization breaking. Measurements of dijet cross‐sections 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 diffractive dijet cross sections in DIS agree well with the QCD predictions, supporting the QCD factorization for DIS. This is not the case for the diffractive dijet cross sections in photoproduction, which are significantly suppressed with respect to the expectations from QCD factorization.