Triangular flow of negative pions emitted in PbAu collisions at top SPS energy

The CERES/NA45 experiment measured for the first time triangular flow ($v_{3}$) as a function of transverse momentum ($p_{T}$) of negative pions emitted around midrapidity in central PbAu collisions at $\sqrt{S_{NN}} = 17.3$ GeV. The $v_{3}$ determined within $0.05 < p_{T} < 2$ GeV/c, is corrected for the HBT effects. It is shown that the triangular flow magnitude is smaller by a factor of about 2 than the one measured by the PHENIX experiment at RHIC and the ALICE experiment. Within the analyzed centrality bins, the $v_{3}$ does not shows significant centrality dependence. The obtained $v_{3}(p_{T})$ dependence is well described by a viscous hydrodynamic calculation combined with an UrQMD cascade model in the late stages of the collision.