Anisotropic flow of charged hadrons, pions and (anti-)protons measured at high transverse momentum in Pb-Pb collisions at $\sqrt{s_{\rm NN}}=2.76$ TeV

TL;DR

This paper measures azimuthal anisotropic flow coefficients for various particles in Pb-Pb collisions at 2.76 TeV, revealing particle type dependence and flow fluctuation characteristics up to high transverse momentum.

Contribution

It provides the first detailed measurement of flow coefficients for identified particles at high transverse momentum in heavy-ion collisions.

Findings

Elliptic and triangular flow depend weakly on pT above 8 GeV/c.

Proton flow coefficients are larger than pion coefficients up to 8 GeV/c.

Flow fluctuations have a common origin up to 8 GeV/c.

Abstract

The elliptic, $v_2$, triangular, $v_3$, and quadrangular, $v_4$, azimuthal anisotropic flow coefficients are measured for unidentified charged particles, pions and (anti-)protons in Pb-Pb collisions at $\sqrt{s_{\rm NN}} = 2.76$ TeV with the ALICE detector at the Large Hadron Collider. Results obtained with the event plane and four-particle cumulant methods are reported for the pseudo-rapidity range $|\eta|<0.8$ at different collision centralities and as a function of transverse momentum, $p_{\rm T}$, out to $p_{\rm T}=20$ GeV/$c$. The observed non-zero elliptic and triangular flow depends only weakly on transverse momentum for $p_{\rm T}>8$ GeV/$c$. The small $p_{\rm T}$ dependence of the difference between elliptic flow results obtained from the event plane and four-particle cumulant methods suggests a common origin of flow fluctuations up to $p_{\rm T}=8$ GeV/$c$. The magnitude of the (anti-)proton elliptic and triangular flow is larger than that of pions out to at least $p_{\rm T}=8$ GeV/$c$ indicating that the particle type dependence persists out to high $p_{\rm T}$.