Abstract
In the extended Nambu–Jona-Lasinio model, the branching fraction of [Formula: see text] is calculated. The contributions from the contact diagram and the diagrams with intermediate axial-vector, vector and pseudoscalar mesons in the ground and first radially excited states are taken into account. It is shown that an axial-vector and vector channel with a contact diagram give a dominant contribution to the branching fraction. The obtained results for the branching fraction [Formula: see text] are in satisfactory agreement with experimental data. A prediction for the differential distribution over the invariant mass of the meson pair [Formula: see text] is given.