Bulk properties of the medium in comparison with models’ predictions in pp collisions at 13 TeV

Abstract

We report a study of the collective properties of the medium produced in pp collisions at 13 TeV. For this study, we used the measurements of the CMS experiment (Sirunyan et al. in Phys Rev D 96:112003, 2017) in the rapidity range $|y| < 1$ and in the transverse momentum ($p_T$) range (0.1–1.7) GeV/c. Modified Hagedorn function with embedded transverse flow velocity and thermodynamically consistent Tsallis distribution functions are used to fit the measured $p_T$ spectra of $\pi ^{\pm }$, $K^{\pm }$ and (anti)-protons and to extract the parameters that characterize the medium created in the collision. The average transverse flow velocity ($<\beta _T>$), extracted from the modified Hagedorn function, is found to decrease with the particle’s mass, the kinetic freeze-out temperature ($T_{0}$) and effective temperature ($T_\mathrm{eff}$) are larger for protons than pions while we observed even higher values for kaons than protons due to their strange quark content. Furthermore, four Monte Carlo event generators, EPOS-LHC, Pythia, QGSJETII-04 and Sibyll2.3d, are used to compare the measurements. The EPOS-LHC and Sibyll2.3d models reproduce the experimental data followed by Pythia, while QGSJETII-04 has greater departure from data for $\pi ^{\pm }$ and $K^\pm$-mesons. In the case of (anti-)protons, only EPOS-LHC predicts well the $p_T$ distribution over the entire $p_T$ range. Although the models have shown good predictions for a particular particle’s $p_T$ spectra or in a range of the spectra, none of them could reproduce the distributions over the entire $p_T$ range for all the particles.