Does quark number scaling breakdown in Pb+Pb collisions at Root_s = 2.76   TeV?
  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. 
Roy A. Lacey, Yi Gu, X. Gong, D. Reynolds, N. N. Ajitanand, J. M.   Alexander, A. Mawi and A. Taranenko (SUNY Stony Brook, C...
nucl-ex nucl-th