Study of the electromagnetic form factors of the nucleons in the timelike region

A bstract The electromagnetic form factors G E and G M of the proton and neutron in the timelike region are extracted in a study of the processes e + e − → pp p ¯ p and e + e − → nn n ¯ n. The reaction amplitude is evaluated within the distorted wave Born approximation, with the interaction of the antinucleon-nucleon (NN) N ¯ N pair taken into account. The latter is constructed within SU (3) chiral effective field theory up to next-to-leading order. An excellent description of the e + e − → NN N ¯ N data in the energy region from the NN N ¯ N threshold up to center-of-mass energies E cm = 2. 2 GeV is achieved. Results for the electromagnetic form factors G E, G M, G E / G M, and the subtracted effective form factors, G osc, are provided. These can be helpful for further studies of the properties of the nucleons.