Comparative Analysis of Jet and Underlying Event Properties Across Various Models as a Function of Charged Particle Multiplicity at 7 TeV

TL;DR

This paper compares various Monte Carlo models' predictions of jet and underlying event properties in 7 TeV proton-proton collisions with CMS experimental data, highlighting the strengths of models with collective flow effects.

Contribution

It provides a detailed comparison of multiple MC generators, emphasizing the impact of collective flow modeling on accurately reproducing experimental results.

Findings

EPOS4_Hydro, EPOSLHC, and Pythia8 accurately reproduce data across various observables.

EPOSLHC performs best for high $p_T$ charged jet rates.

Models with collective flow effects better match experimental jet and underlying event properties.

Abstract

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.