Measurement of the properties of inelastic p-p events with the ATLAS detector

The measurement of the properties of proton-proton interactions at center-of-mass energies ranging from 900 GeV (injection energy) to 7 TeV in the ATLAS detector are presented for a well defined kinematic region. Using charged particles (unfolded and corrected from observed tracks for detector effects), spectra in transverse momentum, pseudo-rapidity and particle density are studied in an inclusive manner. In addition, the momentum flow and angular distribution with respect to a high pT reference track is investigated to study the transition to the underlying event in high pT collisions. The results are compared to Monte Carlo models and have been used to derive Monte Carlo tunes using the first ATLAS measurements from LHC to constrain model parameters.