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

The p(T)-differential non-linear flow modes, v(4,22), v(5,32), v(6, 33) and v(6,222) for pi(+/-), K-+/-, K-S(0), p + (p) over bar, Lambda + (Lambda) over bar and phi-meson have been measured for the first time at root SNN = 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.