Minimum Bias and Underlying Event studies with a Monte Carlo tune for pp events with the ATLAS detector

Charged particle distributions from p p collisions at 0.9 and 7 TeV measured with the ATLAS detector are presented. The distributions are shown in diffraction suppressed and diffraction en- hanced minimum bias event samples. The fraction of events in the diffraction enhanced sample to the inclusive sample is used to constrain the relative diffractive cross section. Underlying event distributions, where the charged particle density in a region transverse to the hard interaction is plotted as a function of the transverse momentum of the leading charged particle, are also pre- sented. In addition a new ATLAS tune to the diffraction suppressed minimum bias and underlying event data is presented.