Mass and width of theρ0from anS-matrix approach toe+e−→π+π−

We determine the mass and width of the ${\mathrm{\rho }}^0$ meson by applying the S-matrix formalism to the reaction ${\mathit{e}}^{+}$ ${\mathit{e}}^{\mathrm{-}}$→${\mathrm{\pi }}^{+}$ ${\mathrm{\pi }}^{\mathrm{-}}$ in the timelike region. We obtain ${\mathit{M}}_{\mathrm{\rho }}$=(757.5±1.5) MeV and ${\mathrm{\Gamma }}_{\mathrm{\rho }}$=(142.5±3.5) MeV, which are significantly smaller than the values quoted by the Particle Data Group. These values are almost independent of the specific form used to model the background.