Elliptic flow of hadrons in equal-velocity quark combination mechanism in relativistic heavy-ion collisions

Abstract

We apply a quark combination model with equal-velocity combination (EVC) approximation to study the elliptic flow ($v_2$) of hadrons in heavy-ion collisions in a wide collision energy range ($\sqrt{s_{NN}}=$ 27 - 5020 GeV). Utilizing the simple relationship between $v_2$ of hadrons and those of quarks under EVC, we find that $v_2$ of up/down quarks obtained by experimental data of proton is consistent with that obtained by data of $\hat{I}›$ and $\hat{I}ž$. $v_2$ of strange quarks obtained by data of $\hat{I}\text{c◯}$ is consistent with that obtained by data of $\hat{I}›$ and $\hat{I}ž$, and at RHIC energies it is also consistent with that obtained by data of $\ddot{I}•$. This means that $v_2$ of these hadrons have a common quark-level source. Using data of $D^0$, we obtain $v_2$ of charm quarks with $p_T\lesssim 6$ GeV/c. We find that under EVC charm quark dominates $v_2$ of $D$ mesons at low $p_T$ but light-flavor quarks significantly contribute to $v_2$ of $D$ mesons in the range $3\lesssim p_T\lesssim 8$ GeV/c. We predict $v_2$ of charmed baryons $\hat{I}{›}_c^{+}$ and $\hat{I}{ž}_c^0$ which show a significant enhancement at intermediate $p_T$ due to the double contribution of light-flavor quarks. The properties of the obtained quark $v_2$ under EVC are studied and a regularity for $v_2$ of quarks as the function of $p_T/m$ is found.

12 pages, 11 figures