Jet modification in absence of QGP-medium: the role of multiparton interactions and color reconnection

TL;DR

This study investigates how multiparton interactions and color reconnection in PYTHIA 8 can modify jet shape and fragmentation in high-energy proton-proton collisions, mimicking effects usually attributed to quark-gluon plasma formation.

Contribution

It demonstrates that MPI and CR mechanisms in PYTHIA 8 can significantly alter jet observables, providing insights into non-QGP effects in small collision systems.

Findings

MPI and CR increase jet production rates.

MPI and CR cause significant modifications in jet shape and fragmentation.

Modification correlates with the number of MPIs and gluonic contributions.

Abstract

Recent studies of high-multiplicity events in small collision systems (proton-proton and proton-lead) have drawn research interest towards the possibility of the formation of partonic medium in such systems. One of the important consequences of the formation of dense partonic medium is quenching of high-momentum final-state particles resulting in several experimental observations such as suppression in nuclear modification factor $R_{\rm AA}$, modification of jet shape observable $\rho(r)$ and jet fragmentation ($z^{\rm ch}$) distributions, etc. In this work, we study $\rho(r)$ and $z^{\rm ch}$ for inclusive charged-particle jets in proton-proton (pp) collisions at $\sqrt{s}$~=~13~TeV using PYTHIA~8 Monash~2013 Monte Carlo simulation. We show that the color reconnection (CR) and multiparton interaction (MPI) mechanisms in PYTHIA~8 can lead to an increased rate of jet production. We also find that the mechanisms of MPI and CR and change in the gluonic contribution in high-multiplicity events result in significant modification of $\rho(r)$ and $z^{\rm ch}$ compared to those in minimum bias events for 10~$<p_{\rm T,\,jet}^{\rm ch}<$~20~GeV/$c$. We notice a direct connection of $\langle N_{\rm MPI}\rangle$ and gluonic contribution with the amount of modification in $\rho(r)$ -- the larger the number of MPIs and/or gluonic contribution, the larger the amount of modification of $\rho(r)$.