Differential Cross Sections for Single Diffractive Dissociation using ALFA

A dedicated sample of Large Hadron Collider proton-proton (\pp{}) collision data at centre-of-mass energy 8 TeV is used to study inclusive single diffractive dissociation, $pp \rightarrow Xp$. The intact final state proton is reconstructed in the ATLAS ALFA forward spectrometer, while charged particles from the dissociated system $X$ are measured in the central detector components. Cross sections are measured differentially as functions of the proton fractional energy loss $\xi$, the four momentum transfer squared $\t$, and $\Delta \eta$, a variable that characterises the rapidity gap separating the proton and the system $X$. The data are consistent with an exponential $t$ dependence, ${\rm d} \sigma / {\rm d} t \propto e^{Bt}$ with slope parameter $B = 7.60 \pm 0.32 \ {\rm GeV^{-2}}$. Interpreted in the framework of Regge phenomenology, the $\xi$ dependence leads to a Pomeron intercept of $\alpha(0) = 1.07 \pm 0.09$.