Non-linear flow modes of identified particles in Pb-Pb collisions at √sNN = 5.02 TeV

Abstract The p T-differential non-linear flow modes, v 4,22, v 5,32, v 6,33 and v 6,222 for π ± , K ± , $$ {\mathrm{K}}_{\mathrm{S}}^0 $$ K S 0 , p + $$ \overline{\mathrm{p}} $$ p ¯ , Λ + $$ \overline{\Lambda} $$ Λ ¯ and ϕ-meson have been measured for the first time at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5.02 TeV in Pb-Pb collisions with the ALICE detector at the Large Hadron Collider. The results were obtained with a multi-particle technique, correlating the identified hadrons with reference charged particles from a different pseudorapidity region. These non-linear observables probe the contribution from the second and third order initial spatial anisotropy coefficients to higher flow harmonics. All the characteristic features observed in previous p T-differential anisotropic flow measurements for various particle species are also present in the non-linear flow modes, i.e. increase of magnitude with increasing centrality percentile, mass ordering at low p T and particle type grouping in the intermediate p T range. Hydrodynamical calculations (iEBE-VISHNU) that use different initial conditions and values of shear and bulk viscosity to entropy density ratios are confronted with the data at low transverse momenta. These calculations exhibit a better agreement with the anisotropic flow coefficients than the non-linear flow modes. These observations indicate that non-linear flow modes can provide additional discriminatory power in the study of initial conditions as well as new stringent constraints to hydrodynamical calculations.