Measurement of the Underlying Event in Jet Topologies using Charged Particle and Momentum Densities

A study of Underlying Events with the CMS detector under nominal and start-up conditions is discussed. Using charged particle densities in charged particle jets, it will be possible to discriminate between various QCD models with different multiple parton interaction schemes, which correctly reproduce Tevatron data but give different predictions when extrapolated to the LHC energy. This will permit improving and tuning Monte Carlo models at LHC start-up, and opens prospects for exploring QCD dynamics in proton-proton collisions at 14 TeV.