Maciej Marek Trzebinski (Polish Academy of Sciences)
The total pp cross section is a fundamental property of the strong interaction which can not be calculated in perturbative QCD but only described based on phenomenological models. The ATLAS collaboration has explored the total proton-proton cross section, using measurements of the total inelastic proton-proton cross sections and of the diffractive part of the inelastic cross section in special data sets taken with low beam currents. The measurements have been performed at center of mass energies of 7TeV and 13TeV, using special forward scintillators or the calorimeters. Studies of the production of di-jets accompanied by a large rapidity gap are presented, which is also used to estimate the "gap survival probability" in hadron-hadron collisions. Finally, a measurement of exclusive production of dileptons in 7 TeV pp collisions is presented. The results show significant deviations from the pure QED prediction, which can be explained by photon coherence and proton rescattering effects. The total cross section can be also extracted from a measurement of the differential elastic cross section using the optical theorem. The ATLAS Collaboration has collected 0.5 /nb of elastic data in a dedicated run with high beta* optics at 8 TeV centre-of-mass energy with the ALFA Roman Pot detector in order to perform this measurement.
Elizaveta Shabalina (University of Gottingen)