Measurement of the Inelastic Proton-Proton Cross-Section at \sqrt{s} = 7 TeV with the ATLAS Detector.

A first measurement of the inelastic cross-section is presented for proton-proton collisions at a center of mass energy $\sqrt{\rm s} = 7$\,TeV using the ATLAS detector at the Large Hadron Collider. In a dataset corresponding to an integrated luminosity of 20$\,\mu$b, events are selected by requiring hits on scintillation counters mounted in the forward region of the detector. An inelastic cross-section of $60.3 \pm 2.1$\,mb is measured for $\xi > 5 \times 10^{-6}$, where $\xi = M_{X}^2/s$ is calculated from the invariant mass, $M_X$, of hadrons selected using the largest rapidity gap in the event. For diffractive events this corresponds to requiring at least one of the dissociation masses to be larger than $15.7$\,GeV.