S-matrix approach to two-pion production in e+e- annihilation and tau decay.

Abstract

Based on the S-matrix approach, we introduce a modified formula for the ${\mathrm{\ensuremath{\pi}}}^{\ifmmode\pm\else\textpm\fi{}}$ electromagnetic form factor which describes very well the experimental data in the energy region 2${\mathit{m}}_{\mathrm{\ensuremath{\pi}}}$\ensuremath{\le}\ensuremath{\surd}s\ensuremath{\le}1.1 GeV. Using the CVC hypothesis we predict B(${\mathrm{\ensuremath{\tau}}}^{\mathrm{\ensuremath{-}}}$\ensuremath{\rightarrow}${\mathrm{\ensuremath{\pi}}}^{\mathrm{\ensuremath{-}}}$${\mathrm{\ensuremath{\pi}}}^{0}$${\ensuremath{\nu}}_{\mathrm{\ensuremath{\tau}}}$)=(24.75\ifmmode\pm\else\textpm\fi{}0.38)%, in excellent agreement with recent experiments. \textcopyright{} 1996 The American Physical Society.