Production and nuclear modification factors of pions, kaons and protons in pp and AA collisions at the LHC

Abstract

In heavy-ion collisions at relativistic energies, a deconfined strongly-interacting state of matter is created. The elementary degrees of freedom of this state are the ones of Quantum Chromodynamics (QCD), namely quarks and gluons, hence its name Quark-Gluon Plasma (QGP). At the CERN Large Hadron Collider (LHC), protons and heavy-ions are accelerated at the highest energies ever achieved in the laboratory. The detector of A Large Ion Collider Experiment (ALICE) at the LHC, was especially designed to study the physics of the QGP produced in heavy-ion collisions. The “bulk” of the produced particles is constituted by hadrons containing only the “light” flavor quarks (u, d, s). Most of these hadrons are produced at low transverse momentum (pT) and originate from soft QCD processes. In this work, the production of π±, K±, p and p has been measured in Pb–Pb collisions at √sNN = 5.02 TeV and in inelastic pp collisions at √s = 5.02 TeV. To this end, the excellent PID performance of the ALICE Time-Of-Flight detector (TOF) were exploited. The pT spectra of pions, kaons and protons have been measured in a wide momentum range (from 100 MeV/c to 12 GeV/c) and as a function of centrality. Based on this measurements, it was possible to characterize the medium formed in the collision. Particle production at low pT exhibits features typical of the collective evolution of a strongly interacting medium. At this energy the largest radial flow velocity is observed. The thermal properties of the medium can be accessed by studying the relative particle abundances in the framework of Statistical Hadronization Models. The Nuclear Modification Factor was computed to quantify the effect of parton energy loss in the QGP on high-pT particle production. The results are interpreted in comparison to predictions from state-of-the-art models and to similar measurements at the LHC.