Comparative analysis of charged particle distributions and model predictions for underlying events with track-based selection in 13 TeV pp collisions

Abstract

In this study, we conduct a comprehensive analysis of charged particle distributions that are particularly sensitive to underlying events. We employ simulations from three distinct models: EPOS4, Pythia8.3, and QGSJETII. These simulations are subsequently compared to experimental measurements obtained by the ATLAS experiment in proton–proton collisions at a center-of-mass energy of \(\sqrt{s} = 13\) TeV. The analysis is conducted under specific kinematic conditions, with a focus on physical observables within the region defined by \(|\eta | < 2.5\) and \(p_{T} > 0.5\) GeV. A comparison of model predictions with data reveals that EPOS4 and Pythia8.3 consistently provide favorable results for various distributions, including mean charged particle densities, mean multiplicities, and average transverse momentum. The QGSJETII-04 model performs well at low \(p^{lead}_{\perp }\) and low \(N_{ch}\), but under-predicts data in some distributions. EPOS4 stands out as having more accurate results, attributed to its detailed treatment of parton saturation and hydrodynamic effects, while Pythia8.3 benefits from parameters such as color reconnection and multi-parton interaction. The QGSJET focuses on cosmic-ray air showers and less on collective effects, highlighting the need for careful model selection to accurately represent particle collision physics. Furthermore, we employ a thermodynamically consistent Tsallis distribution function to extract parameter values for comparison purposes. Our findings reveal that the parameter values extracted from the fit function align more closely with the data for the EPOS4 and Pythia8.3 models, indicating that these two models provide a better representation of the experimental observations as compared to QGSJETII-04.