Cross section and polarization observables for the reaction $e^{+}+e^{-}\to a_1(1260)+\pi$

A model independent formalism for the electron positron annihilation reaction $e^{+}+e^{-}\to a_1(1260)+\pi$ has been derived. The differential and total cross sections and the elements of the spin–density matrix of the $a_1$-meson were calculated in terms of the electromagnetic form factors of the corresponding ${\gamma }^{\ast }{a}_1\pi$ current. Simple models of $a_1$ form factors have been fitted to the available cross section data and they allow to give numerical predictions for the different observables.