Angular Distribution of Processes e⁺e^-→τ⁺τ^-,τ^-→a₁^-υ_τ,a₁^-→ρπand Characteristics of a₁Meson

Abstract：

The density matrix and the helicity formalism of the angular distribution of the processes e ⁺e ^-→ τ ⁺ τ ^-, τ ^-→a ₁ ^- υ _τ,a ₁ ^-→ ρπare obtained. The helicity amplitude ratios corresponding to the form factors of the W-a ₁transition and the strong interaction vertex a ₁ ρπcan be determined by the sectionalized fitting method. Then a model-independent method is given for precisely determining the mass and the width of the very broad resonance a ₁.