https://doi.org/10.1140/epjc/s10052-024-13416-y
Regular Article
The 
ratio in PbAu collisions at 
17.3 GeV: a hint of a hydrodynamic behavior
1
Nuclear Physics Institute, Czech Academy of Sciences, 25068, Řež, Czech Republic
2
Joint Institute of Nuclear Research, 141980, Dubna, Moscow Region, Russia
3
Institut für Kernphysik, Universität Münster, 48149, Münster, Germany
4
Institut für Kernphysik, Johann Wolfgang Goethe-Universität Frankfurt, 60438, Frankfurt, Germany
5
Max-Planck-Institut für Kernphysik, 69117, Heidelberg, Germany
6
Nuclear Physics Institute, Czech Academy of Sciences, 25068, Řež, Czech Republic
7
Czech Technical University in Prague, Faculty of Nuclear Sciences and Physical Engineering, 11519, Prague, Czech Republic
8
Research Division and Extreme Matter Institute (EMMI), GSI Helmholtzzentrum für Schwerionenforschung, 64291, Darmstadt, Germany
9
Physikalisches Institut, Universität Heidelberg, 69120, Heidelberg, Germany
10
Department of Particle Physics, Weizmann Institute, 76100, Rehovot, Israel
11
Department for Physics and Astronomy, SUNY Stony Brook, 11974, Stony Brook, NY, USA
12
Institute of Physics, University of Tsukuba, Tsukuba, Japan
13
Physics Department, University of California, 94720-7300, Berkeley, CA, USA
14
“VINČA” Institute of Nuclear Science-National Institute of the Republic of Serbia, University of Belgrade, Mike Petrovića Alasa 12-14, Vinča, 11351, Belgrade, Serbia
15
Strong-coupling Physics International Research Laboratory, Huzhou University, Huzhou, China
16
Faculty of Science, P. J. Šafárik University, Kosice, Slovakia
17
Instrumentation Division, Brookhaven National Laboratory, 11973-5000, Upton, NY, USA
Received:
6
June
2024
Accepted:
25
September
2024
Published online:
21
October
2024
The Fourier harmonics, 
and 
of negative pions are measured at center-of-mass energy per nucleon pair of 
= 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 
from 0.05 GeV/c to more than 2 GeV/c. This is the first measurement of the ratio as a function of transverse momentum at SPS energies, that reveals, independently of the hydrodynamic models, hydrodynamic behavior of the formed system. For 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 Author(s) 2024
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Funded by SCOAP3.
