Charged-pion production in Au+ Au collisions at √sNN=2.4GeV : HADES Collaboration

AbstractWe present high-statistic data on charged-pion emission from Au + Au collisions at$$\sqrt{s_{\mathrm{NN}}} = 2.4~\hbox {GeV}$$sNN=2.4GeV(corresponding to$$E_{beam} = 1.23~\hbox {A GeV}$$Ebeam=1.23A GeV) in four centrality classes in the range 0–40% of the most central collisions. The data are analyzed as a function of transverse momentum, transverse mass, rapidity, and polar angle. Pion multiplicity per participating nucleon decreases moderately with increasing centrality. The polar angular distributions are found to be non-isotropic even for the most central event class. Our results on pion multiplicity fit well into the general trend of the available world data, but undershoot by$$2.5~\sigma $$2.5σdata from the FOPI experiment measured at slightly lower beam energy. We compare our data to state-of-the-art transport model calculations (PHSD, IQMD, PHQMD, GiBUU and SMASH) and find substantial differences between the measurement and the results of these calculations.