  In this study, a comprehensive analysis of jets and underlying events as a
function of charged particle multiplicity in proton-proton (pp) collisions at a
center-of-mass energy of $\sqrt{s} = 7$ TeV is presented. Various Monte Carlo
(MC) event generators, including Pythia8.308, EPOS1.99, EPOSLHC,
EPOS4$_{Hydro}$, and EPOS4$_{noHydro}$, are employed to predict particle
production. The predictions from these models are compared with experimental
data from the CMS collaboration. The charged particles are categorized into
those associated with underlying events and those linked to jets. The analysis
is restricted to charged particles with $|\eta| < 2.4$ and $p_{T} > 0.25$
GeV/c. Upon comparing the MC predictions with CMS data, it is observed that
EPOS$4_{Hydro}$, EPOSLHC, and Pythia8 consistently reproduce the experimental
results for all charged particles, underlying events, intrajet, and leading
charged particles. For charged jet rates with $p_{T}^{ch.jet} > 5$ GeV/c,
EPOS4$_{Hydro}$ and Pythia8 perform exceptionally well. In the case of charged
jet rates with $p_{T}^{ch.jet} > 30$ GeV/c, EPOSLHC reproduces satisfactorily
good results, while EPOS4$_{Hydro}$ exhibits good agreement with the data at
higher charged particle multiplicities as compared to the other models. This
can be attributed to the conversion of energy into flow when "Hydro=on,"
leading to an increase in multiplicity. EPOSLHC model described the data well
due to the new collective flow effects, correlated flow treatment, and
parametrization as compared to the EPOS1.99. However, the examination of the
jet $p_{T}$ spectrum and normalized charged $p_{T}$ density reveals that
EPOS4$_{Hydro}$, EPOS4$_{noHydro}$, and EPOSLHC exhibit good agreement with the
experimental results, while Pythia8 and EPOS1.99 do not perform as well due to
the lack of correlated flow treatment.
