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The Fourier harmonics, v 2 and v 3 of negative pions are measured at center-of-mass energy per nucleon pair of s NN = 17.3 GeV around midrapidity by the CERES/NA45 experiment at the CERN SPS in 0–30% central PbAu collisions with a mean centrality of 5.5%. The analysis is performed in two centrality bins as a function of the transverse momentum p T from 0.05 GeV/ c to more than 2 GeV/ c . This is the first measurement of the v 3 1 / 3 / v 2 1 / 2 ratio as a function of transverse momentum at SPS energies, that reveals, independently of the hydrodynamic models, hydrodynamic behavior of the formed system. For p T above 0.5 GeV/ c , the ratio is nearly flat in accordance with the hydrodynamic prediction and as previously observed by the ATLAS and ALICE experiments at the much higher LHC energies. The results are also compared with the SMASH-vHLLE hybrid model predictions, as well as with the SMASH model applied alone.

The Fourier harmonics,$$v_2$$v 2 and$$v_3$$v 3 of negative pions are measured at center-of-mass energy per nucleon pair of$$\\sqrt{s_{\\textrm{NN}}}$$s NN = 17.3 GeV around midrapidity by the CERES/NA45 experiment at the CERN SPS in 0–30% central PbAu collisions with a mean centrality of 5.5%. The analysis is performed in two centrality bins as a function of the transverse momentum$$\\mathrm {p_{\\textrm{T}}}$$p T from 0.05 GeV/ c to more than 2 GeV/ c . This is the first measurement of the$$v^{1/3}_{3}/v^{1/2}_{2}$$v 3 1 / 3 / v 2 1 / 2 ratio as a function of transverse momentum at SPS energies, that reveals, independently of the hydrodynamic models, hydrodynamic behavior of the formed system. For$$\\mathrm {p_{\\textrm{T}}}$$p T above 0.5 GeV/ c , the ratio is nearly flat in accordance with the hydrodynamic prediction and as previously observed by the ATLAS and ALICE experiments at the much higher LHC energies. The results are also compared with the SMASH-vHLLE hybrid model predictions, as well as with the SMASH model applied alone.

Abstract The Fourier harmonics,$$v_2$$v 2 and$$v_3$$v 3 of negative pions are measured at center-of-mass energy per nucleon pair of$$\\sqrt{s_{\\textrm{NN}}}$$s NN = 17.3 GeV around midrapidity by the CERES/NA45 experiment at the CERN SPS in 0–30% central PbAu collisions with a mean centrality of 5.5%. The analysis is performed in two centrality bins as a function of the transverse momentum$$\\mathrm {p_{\\textrm{T}}}$$p T from 0.05 GeV/c to more than 2 GeV/c. This is the first measurement of the$$v^{1/3}_{3}/v^{1/2}_{2}$$v 3 1 / 3 / v 2 1 / 2 ratio as a function of transverse momentum at SPS energies, that reveals, independently of the hydrodynamic models, hydrodynamic behavior of the formed system. For$$\\mathrm {p_{\\textrm{T}}}$$p T above 0.5 GeV/c, the ratio is nearly flat in accordance with the hydrodynamic prediction and as previously observed by the ATLAS and ALICE experiments at the much higher LHC energies. The results are also compared with the SMASH-vHLLE hybrid model predictions, as well as with the SMASH model applied alone.

The Fourier harmonics, \\(v_2\\) and \\(v_3\\) of negative pions are measured at center-of-mass energy per nucleon pair of \\(s_NN\\)= 17.3 GeV around midrapidity by the CERES/NA45 experiment at the CERN SPS in 0--30\\% central PbAu collisions with a mean centrality of 5.5\\%. The analysis is performed in two centrality bins as a function of the transverse momentum \\(p_T\\) from 0.05 GeV/\\(c\\) to more than 2 GeV/\\(c\\). This is the first measurement of the \\(v^1/3_3/v^1/2_2\\) ratio as a function of transverse momentum at SPS energies, that reveals, independently of the hydrodynamic models, hydrodynamic behavior of the formed system. For \\(p_T\\) above 0.5 GeV/\\(c\\), the ratio is nearly flat in accordance with the hydrodynamic prediction and as previously observed by the ATLAS and ALICE experiments at the much higher LHC energies. The results are also compared with the SMASH-vHLLE hybrid model predictions, as well as with the SMASH model applied alone.

Differential elliptic flow spectra v2(pT) of \\pi-, K0short, p, \\Lambda have been 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. Protons below 0.4 GeV/c are directly identified by dE/dx. At higher pT, proton elliptic flow v2(pT) is derived as a constituent, besides \\pi+ and K+, of the elliptic flow of positive pion candidates. The retrieval requires additional inputs: (i) of the particle composition, and (ii) of v2(pT) of positive pions. For (i), particle ratios obtained by NA49 were adapted to CERES conditions; for (ii), the measured v2(pT) of negative pions is substituted, assuming \\pi+ and \\pi- elliptic flow magnitudes to be sufficiently close. The v2(pT) spectra are compared to ideal-hydrodynamics calculations. In synopsis of the series \\pi- - K0short - p - \\Lambda, flow magnitudes are seen to fall with decreasing pT progressively even below hydro calculations with early kinetic freeze-out (Tf= 160 MeV) leaving not much time for hadronic evolution. The proton v2(pT) data show a downward swing towards low pT with excursions into negative v2 values. The pion-flow isospin asymmetry observed recently by STAR at RHIC, invalidating in principle our working assumption, is found in its impact on proton flow bracketed from above by the direct proton flow data, and not to alter any of our conclusions. Results are discussed in perspective of recent viscous dynamics studies which focus on late hadronic stages.

We present results of a two-pion correlation analysis performed with the Au+Pb collision data collected by the upgraded CERES experiment in the fall of 2000. The analysis was done in bins of the reaction centrality and the pion azimuthal emission angle with respect to the reaction plane. The pion source, deduced from the data, is slightly elongated in the direction perpendicular to the reaction plane, similarly as was observed at the AGS and at RHIC.