# Linear and non-linear flow mode in Pb-Pb collisions at $\sqrt{s_{\rm NN}} =$ 2.76 TeV

## TL;DR

This paper investigates the linear and non-linear flow modes in Pb-Pb collisions at 2.76 TeV, providing insights into initial conditions and medium properties through anisotropic flow measurements.

## Contribution

It presents the first detailed analysis of higher order flow modes ($V_4$, $V_5$, $V_6$) including mode-coupling effects in Pb-Pb collisions at LHC energies.

## Key findings

- Measured higher order flow coefficients for different centralities.
- Compared experimental results with theoretical models.
- Constrained initial geometry and shear viscosity to entropy density ratio.

## Abstract

The second and the third order anisotropic flow, $V_{2}$ and $V_3$, are mostly determined by the corresponding initial spatial anisotropy coefficients, $\varepsilon_{2}$ and $\varepsilon_{3}$, in the initial density distribution. In addition to their dependence on the same order initial anisotropy coefficient, higher order anisotropic flow, $V_n$ ($n > 3$), can also have a significant contribution from lower order initial anisotropy coefficients, which leads to mode-coupling effects. In this Letter we investigate the linear and non-linear modes in higher order anisotropic flow $V_n$ for $n=4$, $5$, $6$ with the ALICE detector at the Large Hadron Collider. The measurements are done for particles in the pseudorapidity range $|\eta| < 0.8$ and the transverse momentum range $0.2 < p_{\rm T} < 5.0$ GeV/$c$ as a function of collision centrality. The results are compared with theoretical calculations and provide important constraints on the initial conditions, including initial spatial geometry and its fluctuations, as well as the ratio of the shear viscosity to entropy density of the produced system.