Exploring the mass radius of He4 and implications for nuclear structure

Abstract

In this study, we determine the mass radius of He4, a very light nucleus, by examining the near-threshold ϕ-meson photoproduction data of the LEPS Collaboration. To assess the gravitational form factor of He4, we employ multiple models for the mass distribution, including Yukawa-type, exponential, Gaussian, and uniform functions. The mass radius of He4 is measured to be 1.70±0.14 fm, which is approximately equal to the charge radius of He4. Surprisingly, in contrast to the findings of the proton, no noticeable discrepancy between the charge radius and the mass radius is noted for the He4 nucleus. The proton and neutron distributions within He4 are likely to be identical, confirming its regular tetrahedral structure in a new way. We propose exploring the difference between charge and mass radii as a new approach to examine the nuclear structure. Published by the American Physical Society 2024