Dalitz plot analysis of the decay D+ ---> K- pi+ pi+ and indication of a low-mass scalar K pi resonance

We study the Dalitz plot of the decay D + → K - π + π + with a sample of 15090 events from Fermilab experiment E791. Modeling the decay amplitude as the coherent sum of known Kπ 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 Χ 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 ′ 19 ′ 43 MeV/c 2 and width 410 ′ 43 ′ 87 MeV/c 2 . The mass and width of the K * 0 (1430) become 1459 ′ 7 ′ 5 MeV/c 2 and 175 ′ 12 ′ 12 MeV/c 2 , respectively. Our results provide new information on the scalar sector in hadron spectroscopy.