Measuring hydrodynamical expansion via the production of identified hadrons in Pb$-$Pb collisions with ALICE

TL;DR

This paper reports on ALICE's measurements of identified hadron production and flow coefficients in Pb-Pb collisions at 5.02 TeV, testing hydrodynamic models and collective behavior across different system sizes.

Contribution

It provides high-precision flow and spectra data for identified hadrons, including the phi meson, and compares these results with advanced hydrodynamic and transport models.

Findings

Mass ordering observed at low p_T

Hydrodynamic models successfully describe spectra up to a few GeV/c

Collective behavior evolves with system size

Abstract

During the LHC Run-2, ALICE has collected data from Pb$-$Pb collisions at $\sqrt{s_{\rm{NN}}}$ = 5.02 TeV. The centrality dependence of identified particle production, including elliptic ($v_{2}$) and higher harmonic flow coefficients ($v_{3},v_{4}$), has been measured. The high-precision measurement of transverse momentum ($p_{\rm T}$) differential elliptic flow of the $\phi$-meson (whose mass is close to that of the proton) allows for a unique testing of mass ordering at low $p_{\rm T}$ as well as baryon and meson grouping at intermediate $p_{\rm T}$. The $p_{\rm T}$-differential hadron spectra are presented and, together with flow coefficients, compared with state-of-the-art calculations from models based on relativistic hydrodynamics coupled with UrQMD. The added transport code is to describe rescattering in the hadronic phase, which has been successful in describing the $p_{\rm T}$-spectra of identified particles up to a few GeV/$c$. Moreover, results from the simultaneous Blast-Wave fit to the $p_{\rm T}$ distributions are compared across multiple collisions energies and system sizes in order to address the evolution of collective behaviour from small systems to large systems.