Evidence for flow in pPb collisions at 5 TeV from v2 mass splitting

One of the strongest signals of collective flow in heavy ion collisions is the fact that the transverse momentum dependence of the elliptical flow coefficient v2 (measuring the azimuthal asymmetry) depends in a very characteristic way on the mass of the observed hadrons. This has been predicted [1] and impressively confirmed experimentally later [2, 3]. Can we also “prove” the existence of flow in small systems like proton-lead collisions, where such a collective behavior has not been expected?