  A new observable, $S_{T}$, is introduced in terms of the sum of the
transverse momentum of charged particles ($\sum_{i} p_{T_{i}}$ ) produced in
proton proton (p$-$p) collisions at LHC energies to probe the underlying events
(UE). The UE are defined as those aspects of proton-proton collisions that are
not attributed to the primary hard scattering process, but rather to the
accompanying interactions of the rest of the proton. The conventional approach
of studying underlying events is usually carried out by defining topological
regions with respect to the leading particle in an event. The transverse region
is generally sensitive to UE and various classifiers have been used to
discriminate the extent of UE activity regions. The production of identified
particles like $\pi^{\pm}$, $K^{\pm}$, p , $K_{S}^{0}$, and $\Lambda^{0}$ are
studied in different ranges of transverse activity classifier in p$-$p
collisions at $\sqrt{s} = 13 $ TeV using pQCD inspired PYTHIA 8 event
generator. A comparative analysis of the identified particle spectra, mean
multiplicity and mean transverse momentum has been carried out with respect to
$S_{T}$ and the performance of this new observable is gauged by comparing the
results with previously defined $R_{T}$ observable.
