Does quark number scaling breakdown in Pb+Pb collisions at Root_s = 2.76 TeV?

TL;DR

This paper investigates whether quark number scaling of the elliptic flow coefficient $v_2$ holds in Pb+Pb collisions at 2.76 TeV, finding that after accounting for a blueshift, the scaling is valid, indicating strong collective behavior.

Contribution

The study demonstrates that quark number scaling of $v_2$ persists at LHC energies when a blueshift correction is applied, highlighting the role of radial flow and plasma properties.

Findings

Quark number scaling of $v_2$ is valid at LHC energies after correction.

LHC collisions exhibit larger mean sound speed and radial flow.

$v_2$ for identified hadrons shows significant increase from RHIC to LHC.

Abstract

The anisotropy coefficient $v_2$, for unidentified and identified charged hadrons [pions ($\pi$), kaons ($K$) and protons ($p$)] measured in Au+Au collisions at $\sqrt{s_{NN}}= 0.20$ TeV (RHIC) and Pb+Pb collisions at $\sqrt{s_{NN}}= 2.76$ TeV (LHC), are compared for several collision centralities ($\text{cent}$) and particle transverse momenta $p_T$. In contrast to the measurements for charged hadrons, the comparisons indicate a sizable increase of $v_2(p_T)$ for $\pi,K$ and $p$, as well as a blueshift of proton $v_2(p_T)$, from RHIC to LHC. When this blueshift is accounted for, the LHC data [for $\pi$, $K$, $p$] show excellent scaling of $v_2({KE}_T)$ with the number of valence quarks ($n_q$), for a broad range of transverse kinetic energies (${KE}_T$) and collision centralities. These observations suggest a larger mean sound speed $<c_s(T)>$ for the plasma created in LHC collisions, and significant radial flow generation after its hadronization.