Left-right splitting of elliptic flow due to directed flow in heavy ion collisions

Abstract

Recently the splitting of elliptic flow $v_2$ at finite rapidities has been proposed as a result of the global vorticity in non-central relativistic heavy ion collisions. In this study, we find that this left-right (i.e., on opposite sides of the impact parameter axis) splitting of the elliptic flow at finite rapidities is a result of the non-zero directed flow $v_1$, with the splitting magnitude $\approx 8v_1(1-3v_2)/(3\pi )$. We also use a multi-phase transport model, which automatically includes the vorticity field and flow fluctuations, to confirm the $v_2$ splitting. In addition, we find that the analytical expectations for the $v_2$ splitting work for the raw $v_2$ and $v_1$ (i.e., before event plane resolutions are applied) measured relative to either the first- or second-order event plane. Since the $v_2$ splitting is mostly driven by $v_1$, it vanishes at zero transverse momentum ($p_{\mathrm{T}}$), and its magnitude and sign may have non-trivial dependencies on $p_{\mathrm{T}}$, centrality, collision energy, and hadron species.

8 pages, 10 figures; v2 splitting results are now shown to 2nd order, added a new section with six figures to show results from the event plane method

References in corpus (4)

• Update of a Multi-Phase Transport Model with Modern Parton Distribution Functions and Nuclear Shadowing
• Calculating the initial energy density in heavy ion collisions by including the finite nuclear thickness
• Using local nuclear scaling of initial condition parameters to improve the system size dependence of transport model descriptions of nuclear collisions
• Directed and elliptic flow of identified hadrons, high-$p_{\mathrm{T}}$ charged hadrons and light nuclei in Au+Au collisions at STAR