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

TL;DR

This paper investigates how color reconnection and hadronic re-scattering influence underlying events in proton-proton collisions at LHC energies, using Pythia 8 simulations across various energies and regions.

Contribution

It provides a detailed analysis of the effects of specific QCD mechanisms like color reconnection and re-scattering on underlying event observables in pp collisions.

Findings

Color reconnection significantly affects charged particle multiplicity.

Hadronic re-scattering impacts the scalar pT sum in underlying events.

Energy dependence observed in underlying event activity across different regions.

Abstract

Underlying events dominate most of the hadronic activity in p$-$p collisions and are spanned from perturbative to non-perturbative QCD, having a sensitivity ranging from the 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 activities has been studied within the framework of Pythia 8 Monte Carlo model, considering the underlying events 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 leading charged particle in towards, away, and transverse region 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 leading particle in p$-$p collisions. The energy dependence of underlying events and their activities in the central and forward region has also been studied. The effect of hadronic re-scattering, color reconnection, and rope hadronization mechanism implemented in Pythia 8 has been studied in details to gain insight into the different processes contributing to underlying events in soft sector.