https://doi.org/10.1140/epja/s10050-025-01645-y
Regular Article - Theoretical Physics
Possible explanation of the irregular energy dependence of the rapidity width of 
mesons observed in Pb+Pb collisions
1
Institut für Theoretische Physik, Goethe-Universität Frankfurt, Max-von-Laue-Str. 1, D-60438, Frankfurt am Main, Germany
2
Frankfurt Institute for Advanced Studies (FIAS), Ruth-Moufang-Str. 1, D-60438, Frankfurt am Main, Germany
3
Helmholtz Research Academy Hesse for FAIR (HFHF), GSI Helmholtzzentrum für Schwerionenforschung GmbH, Campus Frankfurt, Max-von-Laue-Str. 12, 60438, Frankfurt am Main, Germany
4
GSI Helmholtzzentrum für Schwerionenforschung GmbH, Planckstr. 1, D-64291, Darmstadt, Germany
a
bleicher@itp.uni-frankfurt.de
Received:
3
February
2025
Accepted:
10
July
2025
Published online:
23
July
2025
Experimental data from the NA49 collaboration show an unexpectedly steep rise of the rapidity width of the meson as function of beam energy, which was suggested as possible interesting signal for novel physics. In this work we show that the Ultra-relativistic Quantum-Molecular-Dynamics (UrQMD) model is able to reproduce the shapes of the rapidity distributions of most measured hadrons and predicts a common linear increase of the width for all hadrons. Only when following the exact same analysis technique and experimental acceptance of the NA49 and NA61/SHINE collaborations, we find that the extracted value of the rapidity width of the increases drastically for the highest beam energy. We conclude that the observed steep increase of the rapidity width may be a problem of limited detector acceptance and the simplified Gaussian fit approximation.
© The Author(s) 2025
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