Dalitz Plot Analysis of the Decay $D^+\to K^-π^+π^+$ and Study of the $Kπ$ Scalar Amplitudes

We study the decay $D^+\to K^-\pi^+\pi^+$ using data from Fermilab experiment E791. Fitting the Dalitz Plot (15090 events) with an amplitude that is the coherent sum of known $ K \pi $ resonances and a uniform non-resonant term, we obtain a relatively large $\chi^2$ per degree of freedom ($\nu$). If we do not fix the mass and width of the $K^*_0(1430)$ and use Gaussian form factors for this amplitude, the $\chi^2/\nu$ is improved and the mass and the width obtained for the $K^*_0(1430)$ are consistent with PDG values. However, the fit is still unsatisfactory. A more substantial improvement and a good fit result when we also allow for the presence of an additional scalar resonance. The fit mass and width of this resonance are $797\pm 19\pm 43$ MeV/c$^2$ and $410\pm 43\pm 87$ MeV/c$^2$, respectively, and the fit mass and width of the $K^*_0(1430)$ are $1459\pm 7\pm 5$ MeV/c$^2$ and $175\pm 12\pm 12$ MeV/c$^2$, respectively.