Measurement of dijet production in diffractive events with the ATLAS detector

A sample of pp collision data collected under low luminosity conditions at sqrt(s) = 7 TeV by the ATLAS detector at the Large Hadron Collider is used to study diffractive dijet production. Events containing at least two jets with pT > 20 GeV are selected and analysed in terms of variables which discriminate between diffractive and non-diffractive processes. Cross sections are measured differentially in \Delta\eta_F, the size of the observable forward region of pseudorapidity which is devoid of hadronic activity, and in an estimator, \xi˜, of the fractional momentum loss of the proton assuming single diffractive dissociation (pp -> pX). Model comparisons indicate a dominant non-diffractive contribution up to moderately large \Delta\eta_F and small\xi˜, with a diffractive contribution which is significant at the highest \Delta\etaF and the lowest \xi˜. The rapidity gap survival probability is estimated from comparisons of the data in this latter region with predictions based on diffractive parton density functions.