David Anthony Milstead (Stockholm University)
A correct modelling of the underlying event in proton-proton collisions is important for the proper simulation of kinematic distributions of high-energy collisions. The ATLAS collaboration extended previous studies at 7 TeV with a leading track or jet or Z boson by a new study of Drell-Yan events in 1.1 /fb of data collected at a center-of-mass energy of 7TeV. In this new study the distributions of several topological event-shape variables based on charged particles are measured, both integrated and differential in the transverse momentum of the Drell-Yan lepton pair. These measurements are sensitive to the underlying-event as well as the onset of hard emissions. The results have been compared with the predictions of several state-of-the-art MC generators. The collaboration has also performed a first study of the number and transverse-momentum sum of charged particles as a function of pseudorapidity and azimuthal angle in a special data set taken with low beam currents at a center-of-mass energy of 13TeV. The results are compared to predictions of several MC generators.
Dr Elizaveta Shabalina (University of Gottingen)