Elliptic flow of charged pions, protons and strange particles emitted in Pb+Au collisions at top SPS energy

Differential elliptic flow spectra v2(pT) of \pi-, K0short, p, \Lambda were measured at \sqrt(s NN)= 17.3 GeV around midrapidity by the CERN-CERES/NA45 experiment in mid-central Pb+Au collisions (10% of \sigma(geo)). The pT range extends from about 0.1 GeV/c (0.55 GeV/c for \Lambda ) to more than 2 GeV/c. The proton v2(pT) is extracted from the sample of \pi+ candidates using particle ratios from NA49 adapted to CERES acceptance and analysis cuts. The v2(pT) spectra are compared to ideal-hydrodynamics calculations. In synopsis, v2 in the series \pi- - K0short - p - \Lambda is seen to fall towards low pT increasingly below the hydro calculations even for kinetic freeze-out at Tf= 160 MeV which effectively suppress the hadronic evolution. The proton v2(pT) shows a downward swing towards low pT with excursions into negative values; the possible impact of a pion-flow isospin asymmetry observed by STAR at RHIC is found not to alter these conclusions. Results are discussed in perspective of recent viscous hydrodynamics studies which focus on the late hadronic stages.