We have compared the experimental data on charged-particle elliptic flow parameter ($v_2$) in Au $+$ Au collisions at midrapidity for $\sqrt{s_{\mathrm{NN}}}=9.2$, $19.6$, $62.4$, and $200$ GeV with results from various models in heavy-ion collisions such as the ultrarelativistic quantum molecular dynamics (UrQMD) model, a multiphase transport model (AMPT), and heavy-ion jet interaction generator (HIJING). We observe that the average $v_2$ ($\langle v_2\rangle$) from the transport model UrQMD agrees well with the measurements at $\sqrt{s_{\mathrm{NN}}}=9.2$ GeV but increasingly falls short of the experimental $\langle v_2\rangle$ values as the beam energy increases. The difference in $\langle v_2\rangle$ is of the order of $60\%$ at $\sqrt{s_{\mathrm{NN}}}=200$ GeV. The $\langle v_2\rangle$ results from HIJING are consistent with zero, while those from AMPT with default settings, a model based on HIJING with additional initial- and final-state rescattering effects included, give a $\langle v_2\rangle$ value of about $4\%$ for all the beam energies studied. This is in contrast to an increase in $\langle v_2\rangle$ with beam energy for the experimental data. A different version of the AMPT model, which includes partonic effects and quark coalescence as a mechanism of hadronization, gives higher values of $\langle v_2\rangle$ among the models studied and is in agreement with the measured $\langle v_2\rangle$ values at $\sqrt{s_{\mathrm{NN}}}=200$ GeV. These studies show that the experimental $\langle v_2\rangle$ has substantial contribution from partonic interactions at $\sqrt{s_{\mathrm{NN}}}=200$ GeV, whose magnitude reduces with decrease in beam energy. We also compare the available data on the transverse momentum and pseudorapidity dependence of $v_2$ to those from these models.

• Received 8 September 2010

DOI:https://doi.org/10.1103/PhysRevC.82.054908