Effect of color reconnection and hadronic re-scattering on underlying events in p–p collisions at LHC energies

Abstract

Underlying events dominate most of the hadronic activity in p–p collisions and are spanned from perturbative to non-perturbative quantum chromodynamics (QCD), with sensitivity ranging from multi-scale to very low-x-scale physics. A detailed understanding of such events plays a crucial role in the accurate understanding of Standard Model (SM) and beyond Standard Model physics. The underlying event activity has been studied within the framework of the Pythia 8 Monte Carlo model, considering the underlying event observables mean charged particle multiplicity density ($\langle d^{2}N /d\eta d\phi \rangle$) and mean scalar $p_T$ sum ($\langle d^{2} \sum p_{T} /d\eta d\phi \rangle$) as a function of the leading charged particle in the towards, away, and transverse regions of p–p collisions at $\sqrt{s}$ = 2.76, 7, and 13 TeV. The towards, away, and transverse regions have been defined on an azimuthal plane relative to the leading particle in p–p collisions. The energy dependence of underlying events and their activity in the central and forward regions have also been studied. The effect of hadronic re-scattering, color reconnection, and rope hadronization mechanism implemented in Pythia 8 has been studied in detail to gain insight into the different processes contributing to underlying events in the soft sector.