The evolution of the near-side peak in two-particle number and transverse momentum correlations in Pb-Pb collisions from ALICE

TL;DR

This paper investigates how two-particle correlations in number and transverse momentum evolve in Pb-Pb collisions, revealing insights into the medium's properties like viscosity, lifetime, and jet-medium interactions.

Contribution

It provides the first detailed measurements of near-side peak evolution in both number and transverse momentum correlations in Pb-Pb collisions, comparing results with theoretical models.

Findings

Near-side peak broadens with centrality, indicating medium effects.

Transverse momentum correlations suggest medium viscosity and relaxation times.

Jet modifications are observed in correlation patterns.

Abstract

Two-particle number and transverse momentum correlations are powerful tools for studying the medium produced in heavy-ion collisions. Correlations in the angular separation of pairs of hadrons can provide information on the medium transport characteristics. In particular, the transverse momentum correlations are sensitive to momentum currents, and provide information about the system life time, the shear viscosity over entropy density ratio ($\eta/s$) and the system relaxation time ($\tau_{\pi}$). Furthermore, the interaction of the jets produced in the initial stages of a collision can be studied using number correlations, by observing the medium-induced modification of the near-side jet peak. Measurements of both sets of correlations from Pb-Pb collisions are reported as a function of centrality. Theoretical interpretations and results from Monte Carlo generators are then confronted with the experimental data.