  A measurement of the underlying event (UE) activity in proton-proton
collisions is performed using events with charged-particle jets produced in the
central pseudorapidity region (abs(eta[jet]) < 2) and with transverse momentum
1<= pt[jet] < 100 GeV. The analysis uses a data sample collected at a
centre-of-mass energy of 2.76 TeV with the CMS experiment at the LHC. The UE
activity is measured as a function of pt[jet] in terms of the average
multiplicity and scalar sum of transverse momenta (pt) of charged particles,
with abs(eta) < 2 and pt > 0.5 GeV, in the azimuthal region transverse to the
highest pt jet direction. By further dividing the transverse region into two
regions of smaller and larger activity, various components of the UE activity
are separated. The measurements are compared to previous results at 0.9 and 7
TeV, and to predictions of several Monte Carlo event generators, providing
constraints on the modelling of the UE dynamics.
