Measurement of higher-order harmonic flow in Pb+Pb collisions at center-of-mass energy = 2.76 TeV

We report on the measurement of higher-order flow harmonics in $\sqrt{s_{NN}}$ = 2.76 TeV PbPb collisions by the CMS experiment at the LHC. The coefficients measured are $v_3$, $v_4$, $v_5$, and $v_6$ of the Fourier decomposition of the azimuthal distribution with respect to the reaction plane and are presented as a function of the transverse momentum $(p_T)$ and centrality for $|\eta| <$ 0.8. The extracted $v_3$ as a function of $p_T$ is largely independent of centrality, while $v_4(p_T)$ is smaller than $v_3$ and increases gradually from central to peripheral collisions. The coefficient $v_5$ shows an approximate quadratic increase as a function of $p_T$, while $v_6$ has the smallest value of any of the coefficients reported here. The ratio $v_4/v_{2}^2$ is measured to be between 1 and 3, depending on centrality and $p_T$. Scaling each $v_n$ coefficient by its associated participant eccentricity $\epsilon_n$ shows $v_2/\epsilon_2$ and $v_3/\epsilon_3$ rising approximately linearly with the number of participating nucleons, while $v_4/\epsilon_4$ and $v_6/\epsilon_6$ fall.