Prediction for minimum bias and the underlying event at LHC energies

In this report we investigate the models employed by PYTHIA and PHOJET Monte Carlo event generators used to describe soft interactions in hadron-hadron collisions. The aim of this study is to predict the important properties of minimum bias and the underlying event at the LHC energy scale. Focusing on a wide range of measurements dominated by soft interactions in proton-proton and proton-anti-proton collisions, one of the aims of this study is to check the consistency of these models when compared to data and evaluate the accuracy of their descriptions of low-p_t processes. Based on comparisons to a wide range of minimum bias and underlying event data we present a tuning for PYTHIA6.214 and compare it to other PYTHIA tunings. Our proposed tuning for PYTHIA6.214 has been used for the ATLAS Data Challenge productions.