Triangular flow of negative pions emitted in PbAu collisions at $\sqrt{s_{NN}} = $ 17.3 GeV

TL;DR

This study measures the triangular flow of negative pions in PbAu collisions at 17.3 GeV, providing the first such data at SPS energies and comparing it with higher-energy results and hydrodynamic models.

Contribution

First measurement of differential triangular flow of negative pions at SPS energies, extending the transverse momentum range and comparing with hydrodynamic models.

Findings

Triangular flow magnitude is about half of that at RHIC and LHC energies.

No significant centrality dependence observed within the analyzed range.

Data agree well with viscous hydrodynamic and UrQMD cascade model calculations.

Abstract

Differential triangular flow, $v_3(p_T)$, of negative pions is measured at $\sqrt{s_{NN}}$= 17.3 GeV around midrapidity by the CERES/NA45 experiment at CERN in central PbAu collisions in the range 0-30\% with a mean centrality of 5.5\%. This is the first measurement as a function of transverse momentum of the triangular flow at SPS energies. The $p_T$ range extends from about 0.05 GeV/c to more than 2 GeV/c. The triangular flow magnitude, corrected for the HBT effects, is smaller by a factor of about 2 than the one measured by the PHENIX experiment at RHIC and the ALICE experiment at the LHC. Within the analyzed range of central collisions no significant centrality dependence is observed. The data are found to be well described by a viscous hydrodynamic calculation combined with an UrQMD cascade model for the late stages.