Measurement of mixed higher order flow harmonics in PbPb collisions

The mixed higher order flow harmonics and nonlinear response coefficients of charged particles are measured for the first time as a function of $p_{\rm{T}}$ and centrality in PbPb collisions at $\sqrt{s_{NN}} = 2.76~\mathrm{TeV}$ and $5.02~\mathrm{TeV}$ with the CMS detector. The results are obtained using the scalar product method, and cover a $p_{\rm{T}}$ range from $0.3~\mathrm{GeV}/c$ to $8.0~\mathrm{GeV}/c$, pseudorapidity $|\eta| < 2.4$, and a centrality range of $0-60\%$. At $5.02~\mathrm{TeV}$, results for mixed harmonics are compared to the matching higher order flow harmonics from two-particle correlations, which measure $v_n$ values with respect to the $n$-th order event plane. It is observed that the nonlinear response coefficients of the odd harmonics are larger than the even harmonics ones. The results are compared with hydrodynamic predictions with different shear viscosity to entropy density ratios and different initial conditions.