We extract the mass radius of 4He, a light nucleus, from near-threshold
Ï•-meson photoproduction data of the LEPS Collaboration. We evaluate the
gravitational form factor using several function forms, including the monopole,
dipole, Gauss, and hard-sphere forms. Our analysis reveals that the Gauss and
hard-sphere form factors more accurately describe the differential cross
sections in the small-∣t∣ range near the production threshold. The extracted
mass radii based on the Gauss and hard-sphere form factors are 1.70±0.14 fm
and 1.37±0.08 fm, respectively, with the combined average being smaller
than the charge radius of 4He. More precise and wider ∣t∣-coverage
measurements of the coherent photoproductions of vector mesons off the nuclear
target are necessary to distinguish between different models for describing the
gravitational form factor and provide further insights into the mass radius of
the nucleus.Comment: 6 pages, 3 figure