Elliptic flow of charged and strange hadrons in Pb - Au collisions at 158 AGeV/c measured in CERES experiment

Differential elliptic flow of upsilon_2(p_T) for pi^-, K_s^0, p and Lambda is measured at centerof-mass energy of s**(1/2)_NN=17.3 GeV near the mid-rapidity region in rather central PbAu collisions collected by the CERES/NA45 experiment at CERN. The proton upsilon_2(p_T) is extracted from pi^+ sample and particle ratios measured by NA49 experiment adapted to CERES conditions. The proton upsilon_2(p_T) data show a downward swing towards low p_T with excursions into negative upsilon_2 values which was not observed earlier. The results are compared with corresponding measurements performed at NA49 and STAR experiments as well as with theoretical predictions from ideal relativistic hydrodynamics. The obtained results for baryons are below hydrodynamic predictions even at the kinetic freeze-out temperature of T_f=160 MeV which needs introducing of a viscous hydrodynamics at the late hadronic phase.