Study of the Alpha-particle Monopole Transition form Factor

The ⁴He monopole form factor is studied by computing the transition matrix element of the electromagnetic charge operator between the ⁴He ground-state and the p+³H and n+³He scattering states. The nuclear wave functions are calculated using the hyperspherical harmonic method, by starting from Hamiltonians including two- and three-body forces derived in chiral effective field theory. The electromagnetic charge operator retains, beyond the leading order (impulse approximation) term, also higher order contributions, as relativistic corrections and meson-exchange currents. The results for the monopole form factor are in fair agreement with recent MAMI data. Comparison with other theoretical calculations are also provided. (author)