| Sumario: | The dependence of the rate of proton-proton interactions on the centre-of-mass collision energy, √s, is of fundamental importance for both hadron collider physics and particle astrophysics. The dependence cannot yet be calculated from first principles; therefore, experimental measurements are needed. Here we present the first measurement of the inelastic proton-proton interaction cross-section at a centre-of-mass energy, √s, of 7 TeV using the ATLAs detector at the Large Hadron Collider. 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 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. © 2011 Macmillan Publishers Limited. All rights reserved.
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