Measurement of Underlying Events at CMS

In order to find physics beyond the Stan-
dard Model at a hadron-hadron collider, it is essential
to have Monte-Carlo models that accurately simulate
the complete events recorded in the experiment. To
do this one must not only have an accurate prediction
of the hard-scattering part of the process, but also a
good model for the soft, underlying event (UE) ac-
tivity which mainly consists of beam-beam remnants
(BBR) and the multiple parton interactions (MPI).
A good understanding of the UE at LHC is essential
for searches as well as for precise measurements. The
topological structure of collision events can be used to
define physics observables which are very sensitive to
the UE. From recent studies at CMS it is found that
extrapolation of the description of UE from Tevatron
experiments does not describe the LHC data. The
measurement of .Underlying Events. using leading
track-jet and Drell-Yan process in CMS experiment
will be discussed.