Comparative analysis of charged particle distributions in [formula omitted] collisions at [formula omitted] using Monte Carlo models and fitting functions

Abstract

We conducted a detailed analysis of charged particle transverse momentum distributions using multiple Monte Carlo models – Pythia, HIJING, and QGSJET – compared against experimental data from the ATLAS detector in pp collisions at s=0.9TeV. Pythia emerged as the best among the models under study in representing most of the distributions due to its comprehensive modeling of parton showers, multiparton interactions, and underlying event dynamics, while QGSJET showed good results with the data in some of the distributions only. HIJING, however, was only able to replicate reduced phase-space distributions only.To further explore the collision medium and to extract important information about collective properties, we used the Tsallis-Pareto (TP) type function and the modified Hagedorn (MH) function. The Tsallis function enabled determination of the effective temperature (Teff) and the non-extensivity parameter (n1) while the MH function provided the kinetic freeze-out temperature (T0), transverse flow velocity (<βT>), and a secondary non-extensivity parameter (n2). Our investigation revealed changes in the effective freeze-out parameters based on event conditions. The Teff and <βT> derived from the TP and MH functions respectively exhibited higher values with a tighter pT cut of >500MeV compared to a more inclusive pT cut of >100MeV. Interestingly, the values of the non-extensivity parameters—n1 for the Tsallis function and n2 for the MH function were almost identical across both the experimental data and all three Monte Carlo models. These findings offer invaluable perspectives on the dynamics of charged particles in pp collisions at s=0.9TeV.