Speaker
Description
The $\eta^{\prime}$ meson has a larger mass than the other pseudoscalar mesons in the same nonet of flavor SU(3), due to the effect of the axial U(1) anomaly. Since this effect is closely related to chiral symmetry breaking, various theoretical models predict that the mass of the $\eta^{\prime}$ will decrease significantly in a nuclear medium as chiral symmetry is partially restored.
One of the direct methods for studying in-medium $\eta^{\prime}$ mass spectra is to reconstruct the meson’s invariant mass from the four-momenta of its decay products. We have investigated the $\eta^{\prime}$ mass spectra in the $\gamma$+C reaction via the $\eta^{\prime}\to\gamma\gamma$ decay mode using an electro-magnetic calorimeter BGOegg, which offers world-class mass resolution. We analyzed the line shape of the $\gamma\gamma$ invariant mass spectra in detail, and searched for possible differences between $\eta^{\prime}$ mass inside the nucleus and in vacuum.
In this presentation, we will outline our analysis and report the results.