Production of π 0 and η mesons in carbon-induced relativistic heavy-ion collisions

Dielectron production in12C+12C collisions at 2AGeV with HADES

“…The extrapolation takes into account measured angular distributions, found to be in agreement with UrQMD calculations [4]. The obtained pion multiplicity per number of participating nucleons M π /A part = 0.137 ± 0.015 (A part = 9.0) agrees with previous measurements of charged and neutral pions [5,6] within the quoted error of 11%. The error represents an overall normalization error, dominated by systematic uncertainties in the acceptance and efficiency corrections of the charged-pion analysis.…”

“…A pair cocktail (cocktail A) was calculated from free π 0 , η and ω meson decays only to represent all contributions emitted after the chemical freeze-out of the fireball and compared to our resulting M ee distribution (figure 1(a)). While π 0 and η sources are directly constrained by data [5], the production rate of the ω meson is taken from an m ⊥ -scaling ansatz [7]. In our event generator (PLUTO [8]) meson production was modelled assuming emission from a thermal source with a temperature T = 80 MeV, but no radial expansion velocity.…”

Dielectron production in Ar + KCl collisions at 1.76AGeV

“…6 the excess yields integrated over the mass region M ee = 0.15-0.5 GeV/c 2 from all available reaction systems [6,8,9]. For comparison, inclusive π 0 and η multiplicities measured in photon calorimetry with the TAPS detector [10,11] are plotted as well. Note that all yields are extrapolated to the full solid angle 3 respective average A part in order to compensate for differences in the centrality selection of the various experiments.…”

“…The excess yield, defined in the mass range M ee = 0.15-0.5 GeV/c 2 and extrapolated to 4π , is shown for HADES Ar + KCl and C + C data (solid triangles) [8,9] as well as for DLS data (open triangles) [6]. The π 0 and η results are from TAPS measurements in C + C (squares, solid curves) and Ca + Ca (circles, long-dashed curves) collisions [10,12]. The curves are polynomial fits to these data used to interpolate the multiplicities as a function of bombarding energy (see [11]).…”

“…These new data fully confirmed the earlier DLS result and thereby rechallenged theory to come up with a proper description of pair production at low energies. Comparing the excitation function of the excess pair multiplicity with the known π 0 and η meson production [10][11][12] revealed that the excess scales with bombarding energy very much like the pion yield does, but not at all like the η yield. This finding already suggested baryonic resonances-and mainly the (1232)-as a possible source of the e + e − excess yield.…”