Single dissociative diffraction of protons in $\sqrt {s}$ = 8 TeV collisions with the ATLAS experiment

Abstract

The first LHC-energy differential cross-sections of the single dissociative diffraction process $_{pp}$ $\rightarrow$ $X_p$ are presented as a function of Mandelstam-$t$, fractional proton energy loss $\xi$ and rapidity gaps within the ATLAS inner detector with a coverage of |$\eta$|< 2.5. The measurement is performed using a data sample collected with the ATLAS detector during a dedicated low luminosity run in 2012 with an integrated luminosity of 1.67 nb$^{-1}$ and a centre-of-mass energy of 8TeV. Events are triggered and selected using the ALFA forward detectors, in combination with the ATLAS central detector components, enabling the detection of scattered protons. The fiducial region is chosen to be 0.016 < |$t$| < 0.43 GeV$^2$ and −4.0 < log$_{10} \xi$ < -1.6. The cross-sections within this region are fitted within an interpretation based on Regge theory. The measured $B$ slope within this region is $B$ = 7.60$\pm$0.31 GeV$^{-2}$. The $\xi$ dependence of the cross-section is consistent with that expected from soft Pomeron exchange. The total measured cross-section within the fiducial region is 1.59$\pm$0.13mb. The Pythia8 A3 Monte Carlo tune provides a very good description of the shape of the cross-sections but overestimates the integrated cross-section by approximately 60%