CMS results on underlying event structure

A measurement of the underlying activity in scattering processes with a hard scale in the several GeV region is performed in proton-proton collisions at $\sqrt{s}=0.9$ and 7~TeV, using data collected by the CMS experiment at the LHC. The production of charged particles with pseudorapidity $\lvert \eta\rvert<2$ and transverse momentum $p_{T}>0.5$~GeV/$c$ is studied in the azimuthal region transverse to that of the leading set of charged particles forming a track-jet. A significant growth of the average multiplicity and scalar-$p_{T}$ sum of the particles in the transverse region is observed with increasing $p_{T}$ of the leading track-jet, followed by a much slower rise above a few GeV/$c$. For track-jet $p_{T}$ larger than a few GeV/$c$, the activity in the transverse region is approximately doubled with a centre-of-mass energy increase from 0.9 to 7 TeV. Predictions of several QCD-inspired models as implemented in {\sc pythia} are compared to the data. The first measurement of the charged component of the Underlying Event using the recently proposed jet area over median approach is also presented for proton-proton collisions at $\sqrt{s}=0.9$~TeV.