Polarization effects in the reaction $e^++e^-\to \rho^+ +\rho^- $ and determination of the $\rho -$ meson form factors in the time--like region

Understand

The electron positron annihilation reaction into four pion production has been studied, through the channel $e^++e^-\to \bar \rho+\rho $.

• The differential (and total) cross sections and various polarization observables for this reaction have been calculated in terms of the electromagnetic form factors of the corresponding $\gamma^*\rho\rho $ current.
• The elements of the spin--density matrix of the $\rho -$meson were also calculated.
• Numerical estimations have been done, with the help of phenomenological form factors obtained in the space--like region of the momentum transfer squared and analytically extended to the time-like region.