Speaker
Description
Among the two-body dynamics of the meson-nucleon systems, the interaction between the eta meson ($\eta$) and nucleon ($N$) is not well known although it has been found to be attractive. An experiment [1] is conducted to determine the low-energy $\eta N$ scattering parameters using a special kinematics at the Research Center for Electron Photon Science (ELPH), Tohoku University. The energy and momentum of the emitted proton ($p$) are measured at 0 degrees for $\eta$ photoproduction on the deuteron at incident energies around 0.94 GeV, which gives the low relative momentum between $\eta$ and neutron ($n$) in the final state. Low-energy $\eta n$ scattering is likely to take place in this condition, and the scattering parameters can be determined from the differential cross section as a function of the $\eta n$ invariant mass (corresponding to the relative $\eta n$ momentum) [2]. We present the current status of the experiment.
Recently, a possible $\eta'd$ bound state is theoretically investigated [3]. A structure corresponding to the state can be observed via the $\gamma d\to \eta d$ at incident energies around 1.2 GeV. In case of backward $\eta$ emission, the structure becomes prominent because a background contribution coming from quasi-free single-step $\eta$ emission is highly suppressed. $\eta$ photoproduction on the deuteron has been experimentally studied at ELPH below incident energies of 1.15 GeV. The angular differential cross sections are determined at backward $\eta$ emission angles. We also present the preliminary results for the energy dependence and discuss a possible $\eta'd$ bound state.
[1] T. Ishikawa et al., Acta Phys. Polon. B 48, 1801 (2017).
[2] S.X. Nakamura, H. Kamano, T. Ishikawa, Phys. Rev. C 96, 042201 (R) (2017).
[3] T. Sekihara, H. Fujioka, T. Ishikawa, Phys. Rev. C 97, 045202 (2017).
