Measurements of minimum bias and underlying event distributions and Monte Carlo generator tuning with ATLAS

Measurements of particle and transverse energy distributions are presented from proton-proton collisions at centre-of-mass energies of sqrt(s) = 0.9, 2.36 and 7 TeV. The distributions are measured for charged particles, using the ATLAS tracking detectors, and for charged and neutral particles, using the calorimeters. Several well-defined phases space regions are measured, and inclusive "minimum bias" distributions are presented as well as measurements in regions defined with respect to the highest transverse energy particle in an event, which is sensitive to the underlying event. In addition the energy flow around jet centres and the fragmentation of particles within jets are studied. The data are compared to several Monte Carlo models, including models with parameters tuned to ATLAS data. In particular, we present new tunes of the general purpose MC generators PYTHIA6 and HERWIG which improve upon previous ATLAS tunes, using a wider variety of measurements and/or higher precision data. Systematic studies on the sensitivity of the ATLAS data to the phenomenological model parameters, and on the compatibility of LHC and Tevatron data sets, as well as the effect of the parton distribution functions on the tuned parameters are also presented.