U-spin considerations to guess the unknown time-like neutron form factors

Abstract

The neutron time-like form factors have never been measured. Perturbative QCD, extended vector meson dominance and other models give very different predictions. The available data on Λ form factor and${J \mathord{\left/ {\vphantom {J \Psi }} \right. \kern-\nulldelimiterspace} \Psi } \to B\bar B$ allow an estimation of the neutron time-like form factors according to theU-spin symmetry. At the threshold a large neutron magnetic form factor comes out, likely falling steeper than the proton one.