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

A measurement of the underlying event activity is performed in proton-proton collisionsat sqrt(s)=2.76 GeV, using data collected by the CMS experiment at the LHC.The average multiplicity and scalar-pT sum densities of charged particles in the azimuthalregion transverse to the leading charged particle jet at central pseudorapidities are studied.A steep rise of the underlying event activity is seen with increasing leading jet pTup to a few GeV/c, above which a slower rate of increase is observed. Bydividing the transverse region into the minimum and maximum activity ones on eachside of the leading jet, further information on the dynamic of the UE is obtained. Theresults are compared to predictions of several QCD-inspired models providingconstraints for the tuning parameters involved in these.