Scaling of kinematical, global observables, energy and entropy densities in p + p, p + Pb and Pb + Pb collisions from 0.01 to 13 TeV

Abstract

The multiplicity and average transverse momentum of the charged and identified particles produced in different kinds of colliding systems are an example of global observables used to characterize events over a wide range of energy. Studying these observables provides insights into the collective phenomena and the geometric scaling properties of the systems created in ultra-relativistic p + Pb, Pb + Pb, and even in p + p collisions. The first part of this work presents a study of these variables using different Monte Carlo event generators. It analyzes their sensitivity to find collective phenomena at 0.01, 0.9, 2.76, 7, and 13 TeV, finding a less satisfactory description as the energy decreases. The second part analyzes the average transverse momentum of charged hadrons as a function of the multiplicity for p + p, p + Pb, and Pb + Pb data from the CMS and ALICE experiments. Comparing with Monte Carlo event generators, we look for a possible scaling law of average transverse momentum scaled to the overlap transverse collision area. Additionally, the experimental data are used to compute thermodynamical quantities such as the energy and entropy densities in the Bjorken approach. The results are compared with predictions from EPOS and PYTHIA Monte Carlo event generators. We observe an excellent agreement for ⟨p T⟩ from p + p but not for thermodynamical observables, where a sudden rise in a small ⟨p T⟩ range resembles the lattice quantum chromodynamics results for the ϵ/T 4 as a function of the temperature; however, only the experimental data from p + p show a kind of saturation.