Vector meson dominance and the π0 transition form factor

It is shown that the pi(0) transition form factor F(Q(1)(2), Q(2)(2)) differs substantially from its one-real-photon limit F(Q(1)(2), 0) even for rather small values of Q(2)(2) (approximate to 0.1 GeV2), which cannot be excluded in experiments with one untagged electron. It indicates that the comparison of data with theoretical calculations, which usually assume Q(2)(2) = 0, may be untrustworthy. Our phenomenological model of the pi(0) transition form factor is based on the vector-meson-dominance hypothesis and all its parameters are fixed by using the experimental data on the decays of vector mesons. The model soundness is checked in the two-real-photon limit, where it provides a good parameter-free description of the pi(0) -> 2 gamma decay rate, and in the pi(0) Dalitz decay. The dependence of F(Q(1)(2), Q(2)(2)) on Q(2)(1) at several fixed values of Q(2)(2) is presented and the comparison with existing data performed.