Inelastic proton-proton cross-section at 13 TeV with ATLAS

The inelastic cross-section is a basic property of proton-proton interactions, yet it cannot be calculated from first principles. In 1973 experiments at CERN discovered that it rises with energy—as Heisenberg had predicted. Today, the LHC sets the energy frontier at 13 TeV, and theory predicts an asymptotic “black-disk” limit. In this seminar, I will present a recent measurement of the inelastic cross-section with the ATLAS detector. One of the key ingredients for this study is the rate at which the LHC produces proton collisions—the luminosity. I will illustrate how we measure the LHC luminosity and achieve a percent-level accuracy. Finally, I will describe how this result relates to one of the open questions in cosmic ray physics. "