Study of diffractive processes at the ATLAS Experiment

A data sample of $pp$ collisions corresponding to an integrated luminosity of 6.75 $\mathrm{nb}^{-1}$ was collected at $\sqrt{s} = 7$ TeV using the ATLAS detector at the Large Hadron Collider. Collision events with at least two jets with $p_{\mathrm{T}}>20$ GeV are used to measure the differential cross section of the diffractive dijet production as a function of the rapidity gap size $\Delta\eta^{\mathrm{F}}$, the largest forward region extending from $|\eta| = 4.8$ devoid of particle activity above threshold momentum cuts, and an estimator of the fractional momentum loss of the scattered proton assuming the single diffractive dissociation ($pp \rightarrow pX$), $\tilde\xi^{\pm}$. Comparisons with various Monte Carlo models reveal that though the region of small $\tilde\xi^{\pm}$ and large rapidity gaps is dominated by diffraction, a contribution form non-diffractive events cannot be neglected. The rapidity gap survival probability is estimated based on data to Monte Carlo comparisons in the $-3.2 < \log_{10}\tilde\xi^{\pm} < -2.5$ region of the $\tilde\xi^{\pm}$ distribution with the $\Delta\eta^{\mathrm{F}}>2$ requirement.