From a sample of $1172\pm 61$ $D^{+}\to {\pi }^{-}{\pi }^{+}{\pi }^{+}$ decays, we find $\Gamma (D^{+}\to {\pi }^{-}{\pi }^{+}{\pi }^{+})/\Gamma (D^{+}\to K^{-}{\pi }^{+}{\pi }^{+})=0.0311\mathrm{}\pm {0.0018}_{-0.0026\mathrm{}}^{+0.0016\mathrm{}}$. Using a coherent amplitude analysis to fit the Dalitz plot of these decays, we find strong evidence that a scalar resonance of mass ${478}_{-23\mathrm{}}^{+24\mathrm{}}\pm 17\mathrm{MeV}/c^2$ and width ${324}_{-40\mathrm{}}^{+42\mathrm{}}\pm 21\mathrm{MeV}/c^2$ accounts for approximately half of all decays.

• Received 7 August 2000

DOI:https://doi.org/10.1103/PhysRevLett.86.770