Spin-Isospin Response of the Neutron-Rich Nucleus 8He via the \((p,n)\) Reaction in Inverse Kinematics

A systematic study of the nucleon density distributions of finite nuclei is important for understanding the isospin dependence of the nuclear many-body system. For example, the neutron skin thicknesses are known to be strongly correlated with the density-dependent term of the symmetry energy, and the isospin-dependent term of the nuclear equation of state. In previous works, we have succeeded in extracting the neutron density distributions of stable nuclei such as Sn and Pb isotopes via proton elastic scattering. At the same time we have launched a new project aimed at measuring the Elastic Scattering of Protons with RI beams (ESPRI) with the purpose of the extraction of proton and neutron density distributions of unstable nuclei. We have newly developed and tested unique devices for the ESPRI measurements at NIRSHIMAC in Chiba and GSI in Germany. Finally, we have successfully performed the ESPRI experiment at RIBF in April, 2013. Unlike the case of stable nuclei, however, we have no information on the nuclear charge densities of unstable nuclei. Thus, we have proposed a new method to extract proton and neutron densities via two-energy proton elastic scattering. This method is based on the large difference between the energy dependences of the p-p and p-n interactions. Recently, we performed an experiment to demonstrate this new method using real data of Zr isotopes. In this report, we show the preliminary results of Zr only. For other isotopes (Zr), the analysis is still ongoing. The experiment was performed at RCNP, Osaka University. Polarized proton elastic scattering from Zr and Ni at 200 and 300 MeV was measured by using the Grand Raiden magnetic spectrometer. Figure 1 shows the angular distributions of cross sections (dσ/dΩ) and the analyzing powers (Ay) of Zr(p⃗,p) at 200 and 300 MeV and of Ni(p⃗,p) at 200 MeV. The red lines denote the result of relativistic impulse approximation (RIA) with relativistic-Hartree (RH) densities. The Ni data was used to determine the effective interaction at 200 MeV (solid lines). Using the effective interaction, the proton and neutron densities of Zr were simultaneously searched and the results are denoted by the solid lines in Fig. 1 and 2. The