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, \(\varepsilon_{2}\) and \(\varepsilon_{3}\). 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 \(\varepsilon_{n}\). 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 \(\sqrt{s_{\rm NN}} =\) 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.