Probing non-linearity of higher order anisotropic flow in Pb--Pb collisions

Abstract

The second and the third order anisotropic flow, $V_2$ and $V_3$, are determined by the corresponding initial spatial anisotropy coefficients, ${\epsilon }_2$ and ${\epsilon }_3$, in the initial density distribution. On the contrary, the higher order anisotropic flow $V_n$ ($n>3$), in addition to their dependence on the same order initial anisotropy coefficient ${\epsilon }_n$, have a significant contribution from lower order initial anisotropy coefficients, which leads to mode-coupling effects. In this contribution, we present the investigations on linear and non-linear modes in higher order anisotropic flow ($V_4$, $V_5$ and $V_6$) in Pb--Pb collisions at $\sqrt{s_{\mathrm{NN}}}=$ 2.76 TeV using the ALICE detector at the Large Hadron Collider (LHC). A significant contribution from a non-linear mode is observed. A new observable, the non-linear response coefficient, is measured as well. The comparison to theoretical calculations provides crucial information on dynamic of the created system especially at the freeze-out conditions, which are poorly known from previous flow measurements.

Comments: 4 pages, 3 figures, XXVIth International Conference on Ultrarelativistic Nucleus-Nucleus Collisions (Quark Matter 2017), Chicago, US