Recent results on soft QCD topics from ATLAS

Measurements of the properties of charged particle production are presented from proton-proton collisions at different centre-of-mass energies with focus on the latest results from obtained in 13 TeV collisions in summer 2015. The results are compared to various Monte Carlo event generator models, which describe the data to different extend. Furthermore particle distributions sensitive to the underlying event in proton-proton collisions have been measured and are compared to theoretical models. A preview of the underlying event in 13 TeV collisions is included, which is generally well described by models tuned to lower energies. The effects of space-time geometry in the hadronization phase has been studied in the context of Bose-Einstein correlations. Correlation parameters between charged particles are investigated in p-p collisions at 900 GeV and 7 TeV, up to very high charged-particle multiplicities. The ATLAS Collaboration has also performed a first measurement of the inelastic pp cross-section at 13 TeV using minimum bias scintillators. Precision measurements of the t-differential elastic pp cross section in a dedicated run at 7 TeV centre-of-mass energy with the ALFA Roman Pot detector were used to measure the total cross section as well as the inelastic cross section. A study of diffractive dijet production is presented, where dijet events are studied together with the requirement of a large region of pseudorapidity devoid of hadronic activity. The data are compared with Monte Carlo models and are found to be better described by models including diffraction. The rapidity gap survival probability has also been estimated. The exclusive gamma+gamma -> ll production cross-section in proton-proton collisions at a centre-of-mass energy of 7 TeV has been carried out in the electron and muon channels. Results are found to be consistent with theory calculations only when taking into account proton absorptive effects due to finite proton size.