Transverse momentum distributions of η mesons in near-threshold relativistic heavy ion reactions

Abstract

Transverse momentum spectra of \ensuremath{\eta} mesons have been measured near the free nucleon-nucleon production threshold in the heavy ion reactions $^{40}\mathrm{Ar}$+ $^{\mathrm{nat}}\mathrm{Ca}$, $^{86}\mathrm{Kr}$ + $^{\mathrm{nat}}\mathrm{Zr}$, and $^{197}\mathrm{Au}$+ $^{197}\mathrm{Au}$ at 1.0A GeV and also in $^{40}\mathrm{Ar}$+ $^{\mathrm{nat}}\mathrm{Ca}$ at 1.5A GeV. The measured transverse momentum distributions are compared to model calculations. The relative abundance of \ensuremath{\Delta}(1232) and N(1535) resonances excited in the collision is deduced. A comparison to pion data reveals scaling with the transverse mass of the emitted meson.