Diffractive Deep-Inelastic Scattering

Abstract

New results on diffractive deep-inelastic $e p$ scattering at HERA are presented using data taken in 1994 with the H1 detector. The cross section for diffractive deep-inelastic scattering is measured in terms of a diffractive structure function $F_2^{D(3)}(\beta,Q^2,\xpom)$ over an extended kinematic range. The dependence of $F_2^{D(3)}$ on $\xpom$ is found not to depend on $Q^2$, but to depend on $\beta$. Therefore the $\xpom$ dependence no longer factorizes. The $Q^2$ and $\beta$ dependence of $F_2^{D(3)}$ is analyzed after an integration over the dependence on $\xpom$. For fixed $\beta$ a clear rise with $\log Q^2$ is observed, persisting up to high values of $\beta$. In terms of the Altarelli-Parisi (DGLAP) QCD evolution equations, these scaling violations give clear indications for a gluon dominated process. Subsequently an attempt is made to quantify the parton content of the diffractive exchange using the DGLAP evolution. At the starting scale a ``leading'' gluon distribution is found which contributes about $80 \%$ of the momentum in the diffractive exchange. Measurements of the hadronic final state (energy flow and production of $D^{*}$ mesons) are found to be consistent with the predictions of a model of deep-inelastic electron pomeron scattering using the information on the parton content obtained.