Measurement of the Inelastic Proton-Proton Cross Section at √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 √s = 7 TeV using the ATLAS detector at the Large Hadron Collider. In a dataset corresponding to an integrated luminosity of 20 μb−1, events are selected by requiring hits on scintillation counters mounted in the forward region of the detector. An inelastic cross-section of 60.3 ± 2.1 mb is measured for ξ > 5 × 10−6, where ξ = MX2 /s is calculated from the invariant mass, MX, 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.