Quasinuclear baryonium in e+e- annihilation

The electromagnetic phenomena near the N anti N threshold, the origine of which is connected with the existence of vector N anti N states of quasinuclear nature are discussed. It is shown that a rapid growth and a large value of the nucleon electromagnetic form factor measured in experiments on annihilation of slow antiprotons into e+e- pair due to strong t - channel interaction between p and anti p in the initial state. The possibility of extracting the proton electromagnetic form factor in nonphysical region at q2 < or approximately 4m2 from annihilation anti pd →e+e- + nsub(s) is discussed. In this case as it is shown the amplitude for virtual annihilation anti p''p'' → e+e- corresponds effectively to annihilation of antiproton on free proton, i.e. at q2 > or approximately 4m2. The behaviour of the e+e- → hadrons annihilation cross section near the N anti N threshold is considered in the coupled channel model. The main result is that the existence of N anti N vector bound states near the threshold together with strong attraction between N and anti N in continuum spectrum leads to the appearance of some additional irregularities in the energy dependence of the cross section except resonances of some additional irregularities