A Measurement of the proton-proton inelastic scattering cross-section at $\sqrt{s}$ =7 TeV with the ATLAS detector at the LHC

The first measurement of the inelastic cross-section for proton-proton collisions at a center of mass energy √s = 7 TeV using the ATLAS detector at the Large Hadron Collider is presented. From a dataset corresponding to an integrated luminosity of 20 μb^{−1}, events are selected by requiring activity in scintillation counters mounted in the forward region of the ATLAS detector. An inelastic cross-section of 60.1 ± 2.1 mb is measured for the subset of events visible to the scintillation counters. The uncertainty includes the statistical and systematic uncertainty on the measurement. The visible events satisfy ξ > 5×10^{−6}, where ξ = M^2_X/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. Using an extrapolation dependent on the model for the differential diffractive mass distribution, an inelastic cross-section of 69.1 ± 2.4(exp) ± 6.9(extr) mb is determined, where (exp) indicates the experimental uncertainties and (extr) indicates the uncertainty due to the extrapolation from the limited ξ-range to the full inelastic cross-section.