Measurement of the underlying event activity using charged particle jets in proton-proton collisions at 2.76 TeV

A measurement of the underlying event (UE) activity in proton-proton collisions is performed using events with a leading charged particle jet produced at central pseudorapidity ($|\eta^{\rm{jet}}|<2$) and of transverse momentum in the range of $1$ to $100$ GeV. The analysis uses 0.3 nb$^{-1}$ of integrated luminosity at the centre-of-mass energy of 2.76 TeV at the LHC by the CMS experiment. The UE activity is measured as a function of $p^{\rm{jet}}_{T}$ in terms of the average multiplicity and scalar-$p_{T}$ sum of charged particles with $|\eta|<2$ and $p_{T}>0.5$ GeV in the azimuthal region {\it transverse} to the leading jet direction. By dividing the {\it transverse} region into the minimum and maximum activity sides with respect to the leading jet, further information on the dynamics of the UE is obtained. The measurements are compared to previous results at 0.9 and 7 TeV and to predictions of several QCD-inspired models providing constraints of the parameters involved.