Diffractive Deep-Inelastic Scattering

TL;DR

This paper presents new measurements of diffractive deep-inelastic scattering at HERA, revealing a gluon-dominated parton structure in the diffractive exchange and analyzing its QCD evolution.

Contribution

It provides the first detailed analysis of the parton content of the diffractive exchange using DGLAP evolution and demonstrates a gluon contribution of about 80% at the starting scale.

Findings

The diffractive structure function $F_2^{D(3)}$ depends on $eta$ but not on $ ext{xpom}$.

A clear rise of $F_2^{D(3)}$ with $ ext{log}Q^2$ is observed at fixed $eta$.

The parton analysis indicates a gluon-dominated diffractive exchange.

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.