Inclusive charged hadron elliptic flow in Au + Au collisions at $\sqrt{s_{NN}}$ = 7.7 - 39 GeV

Abstract

A systematic study is presented for centrality, transverse momentum ($p_T$) and pseudorapidity ($\eta$) dependence of the inclusive charged hadron elliptic flow ($v_2$) at midrapidity($|\eta |<1.0$) in Au+Au collisions at $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27 and 39 GeV. The results obtained with different methods, including correlations with the event plane reconstructed in a region separated by a large pseudorapidity gap and 4-particle cumulants ($v_{2}4$), are presented in order to investigate non-flow correlations and $v_2$ fluctuations. We observe that the difference between $v_{2}2$ and $v_{2}4$ is smaller at the lower collision energies. Values of $v_2$, scaled by the initial coordinate space eccentricity, $v_2/\epsilon$, as a function of $p_T$ are larger in more central collisions, suggesting stronger collective flow develops in more central collisions, similar to the results at higher collision energies. These results are compared to measurements at higher energies at the Relativistic Heavy Ion Collider ($\sqrt{s_{NN}}$ = 62.4 and 200 GeV) and at the Large Hadron Collider (Pb + Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV). The $v_2(p_T)$ values for fixed $p_T$ rise with increasing collision energy within the $p_T$ range studied ($<2\mathrm{GeV}/c$). A comparison to viscous hydrodynamic simulations is made to potentially help understand the energy dependence of $v_2(p_T)$. We also compare the $v_2$ results to UrQMD and AMPT transport model calculations, and physics implications on the dominance of partonic versus hadronic phases in the system created at Beam Energy Scan (BES) energies are discussed.

20 pages, 12 figures. Version accepted by PRC

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• Flow harmonics within an analytically solvable viscous hydrodynamic model
• Measurement of the azimuthal anisotropy of neutral pions in PbPb collisions at sqrt(s(NN)) = 2.76 TeV
• Collision energy dependence of elliptic flow splitting between particles and their antiparticles from an extended multiphase transport model
• An experimental review on elliptic flow of strange and multi-strange hadrons in relativistic heavy ion collisions
• Beam energy dependence of the expansion dynamics in relativistic heavy ion collisions: Indications for the critical end point?
• Effects of hadronic mean-field potentials on Hanbury-Brown-Twiss correlations in relativistic heavy-ion collisions
• Beam energy dependent two-pion interferometry and the freeze-out eccentricity of pions in heavy ion collisions at STAR
• Using the $\varphi$-meson elliptic flow to map the strength of partonic interaction
• Strangeness in STAR at RHIC
• What the collective flow excitation function can tell about the quark-gluon plasma
• Scaling of elliptic flow in heavy ion collisions