Underlying Event Studies and Forward Physics at CMS

This paper summarizes the early underlying event and forward measurements of the CMS collaboration using pp collision data up to highest centre of mass energies of $7$ TeV. These studies constitute important tests of the Standard Model and inputs for Monte Carlo tuning. The underlying event in pp interactions is studied measuring the charged multiplicity density and the charged energy density in the transverse region, which is defined considering the azimuthal distance of the reconstructed tracks with respect to the leading track or leading track-jet of the event, the latter being defined from tracks according to different jet clustering algorithms. In addition, we present the measurement of the underlying event using the jet-area/median approach, demonstrating its sensitivity to different underlying event scenarios. The energy flow in the forward direction is measured for minimum bias events and events having a dijet system in the central region. In addition, the absence of energy deposition in the forward region is used to observe diffractive events. We compare our underlying event and forward results with predictions from Monte Carlo event generators tuned to describe the charged particle spectra seen at central rapidities.