Underlying event studies using calorimeter jets with the ATLAS detector at LHC

In this thesis the hadronic structure of proton-proton collisions, the ``underlying event'', is analyzed by studying charged particle distributions. The measurements are based on data taken in March 2010 with the ATLAS detector at a center-of-mass energy of $sqrt{s}=7$ TeV. A proton-proton interaction consist of several components. The hard scattered part is identified using jets and the remaining low scattered reactions are defined as ``underlying event''. By a separation of the azimuthal space with respect to the hard scattered part it is possible to define regions in phase space which are sensitive to the underlying event. In these regions, the charged particle density, the transverse scalar momentum sum density, the mean transverse momentum as well as angular distributions with respect to the hard scattered part are measured. The measurements are compared with various prediction from Monte Carlo simulations. All models shows a significant difference to the measured distributions.