Low-Energy Electron Scattering for Proton and Exotic Nuclei – ULQ2 and SCRIT –

Toshimi Suda (Tohoku University, Sendai, Japan)

I will present recent breakthroughs and future perspectives of electron-scattering studies in Japan.
1) ULQ2 Facility for Proton Charge Radius and Beyond Electron scattering at unprecedentedly low momentum transfers provides a unique tool in nuclear physics, such as for the precise determination of the proton charge radius. At the ULQ2 (Ultra-Low Q²) facility of Tohoku University, we have recently completed a year-long measurement in the lowest-ever momentum-transfer region. I will highlight our efforts to clarify the proton-radius puzzle and present the current status. In addition, I will introduce ongoing programs at ULQ2, including a challenge to determine the neutron charge radius and an attempt to extract the mean-square radius of the neutron distribution in ^{208}Pb through low-momentum-transfer electron scattering.
2) SCRIT Facility for Short-Lived Exotic Nuclei, and What Comes Next Electron scattering on short-lived exotic nuclei, thought impossible, has now become reality. The world’s first facility dedicated to such studies, the SCRIT electron scattering facility at RIKEN, has produced the first-ever electron-scattering data on unstable nuclei. Building on this success, we are now advancing toward an upgrade of the ERIS ISOL for targeting ^{132}Sn and other exotic nuclei. I will present the present status and recent achievements of SCRIT, and outline the unexplored research opportunities that this facility will open. In addition, I would like to discuss our recent discovery of the relation between the fourth moment of the charge density distributions and the mean-square radius of the neutron distributions in nuclei. I believe this idea will open a novel way to study neutron distributions in both stable and short-lived exotic nuclei via electron scattering