1207.1886 (Roy A. Lacey et al.)

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

Roy A. Lacey, Yi Gu, X. Gong, D. Reynolds, N. N. Ajitanand, J. M. Alexander, A. Mawi, A. Taranenko

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 $$ for the plasma created in LHC collisions, and significant radial flow generation after its hadronization.

View original: http://arxiv.org/abs/1207.1886