https://doi.org/10.1140/epja/s10050-022-00796-6
Regular Article - Experimental Physics
Impact of the Coulomb field on charged-pion spectra in few-GeV heavy-ion collisions
1
Institute of Physics, Slovak Academy of Sciences, 84228, Bratislava, Slovakia
2
LIP-Laboratório de Instrumentação e Física Experimental de Partículas, 3004-516, Coimbra, Portugal
3
Institute of Nuclear Physics, Polish Academy of Sciences, 31342, Kraków, Poland
4
Smoluchowski Institute of Physics, Jagiellonian University of Cracow, 30-059, Kraków, Poland
5
GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291, Darmstadt, Germany
6
Technische Universität Darmstadt, 64289, Darmstadt, Germany
7
Institut für Strahlenphysik, Helmholtz-Zentrum Dresden-Rossendorf, 01314, Dresden, Germany
8
Joint Institute of Nuclear Research, 141980, Dubna, Russia
9
Institut für Kernphysik, Goethe-Universität, 60438, Frankfurt, Germany
10
Excellence Cluster ’Origin and Structure of the Universe’, 85748, Garching, Germany
11
Physik Department E62, Technische Universität München, 85748, Garching, Germany
12
II.Physikalisches Institut, Justus Liebig Universität Giessen, 35392, Giessen, Germany
13
Institute for Nuclear Research, Russian Academy of Science, 117312, Moscow, Russia
14
Institute of Theoretical and Experimental Physics, 117218, Moscow, Russia
15
National Research Nuclear University MEPhI (Moscow Engineering Physics Institute), 115409, Moscow, Russia
16
Department of Physics, University of Cyprus, 1678, Nicosia, Cyprus
17
Laboratoire de Physique des 2 infinis Irène Joliot-Curie, Université Paris-Saclay, CNRS-IN2P3, 91405, Orsay, France
18
Nuclear Physics Institute, The Czech Academy of Sciences, 25068, Rez, Czech Republic
19
LabCAF. F. Física, Universidad de Santiago de Compostela, 15706, Santiago de Compostela, Spain
20
Uniwersytet Warszawski, Wydział Fizyki, Instytut Fizyki Doświadczalnej, 02-093, Warszawa, Poland
21
Dipartimento di Fisica and INFN, Università di Torino, 10125, Turin, Italy
22
Coimbra Polytechnic - ISEC, Coimbra, Portugal
23
Technische Universität Dresden, 01062, Dresden, Germany
24
Frederick University, 1036, Nicosia, Cyprus
Received:
3
March
2022
Accepted:
18
July
2022
Published online:
2
September
2022
In nuclear collisions the incident protons generate a Coulomb field which acts on produced charged particles. The impact of these interactions on charged-pion transverse-mass and rapidity spectra, as well as on pion–pion momentum correlations is investigated in Au + Au collisions at 
= 2.4 GeV. We show that the low-
region (
GeV/
) can be well described with a Coulomb-modified Boltzmann distribution that also takes changes of the Coulomb field during the expansion of the fireball into account. The observed centrality dependence of the fitted mean Coulomb potential energy deviates strongly from a 
scaling, indicating that, next to the fireball, the non-interacting charged spectators have to be taken into account. For the most central collisions, the Coulomb modifications of the HBT source radii are found to be consistent with the potential extracted from the single-pion transverse-mass distributions. This finding suggests that the region of homogeneity obtained from two-pion correlations coincides with the region in which the pions freeze-out. Using the inferred mean-square radius of the charge distribution at freeze-out, we have deduced a baryon density, in fair agreement with values obtained from statistical hadronization model fits to the particle yields.
© The Author(s) 2022
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