Dalitz Plot Analysis of the DecayD+→K−π+π+and Indication of a Low-Mass ScalarKπResonance

We study the Dalitz plot of the decay $D^{+}\to K^{-}{\pi }^{+}{\pi }^{+}$ with a sample of 15090 events from Fermilab experiment E791. Modeling the decay amplitude as the coherent sum of known $K\pi$ resonances and a uniform nonresonant term, we do not obtain an acceptable fit. If we allow the mass and width of the $K_0^{*}(1430)$ to float, we obtain values consistent with those from PDG but the ${\chi }^2$ per degree of freedom of the fit is still unsatisfactory. A good fit is found when we allow for the presence of an additional scalar resonance, with mass $797\pm 19\pm 43\mathrm{M}\mathrm{e}\mathrm{V}/{\mathrm{c}}^{\mathrm{2}}$ and width $410\pm 43\pm 87\mathrm{M}\mathrm{e}\mathrm{V}/{\mathrm{c}}^2$. The mass and width of the $K_0^{*}(1430)$ become $1459\pm 7\pm 5\mathrm{M}\mathrm{e}\mathrm{V}/{\mathrm{c}}^{\mathrm{2}}$ and $175\pm 12\pm 12\mathrm{M}\mathrm{e}\mathrm{V}/{\mathrm{c}}^{\mathrm{2}}$, respectively. Our results provide new information on the scalar sector in hadron spectroscopy.