Model independent measurement of S-wave K- pi+ systems using D+ ---> K pi pi decays from Fermilab E791

A model-independent partial-wave analysis of the S-wave component of the K{pi} system from decays of D{sup +} mesons to the three-body K{sup -}{pi}{sup +}{pi}{sup +} final state is described. Data come from the Fermilab E791 experiment. Amplitude measurements are made independently for ranges of K{sup -}{pi}{sup +} invariant mass, and results are obtained below 825 MeV/c{sup 2}, where previous measurements exist only in two mass bins. This method of parametrizing a three-body decay amplitude represents a new approach to analyzing such decays. Though no model is required for the S-wave, a parametrization of the relatively well-known reference P- and D-waves, optimized to describe the data used, is required. The observed phase variation for the S-, P- and D-waves do not match existing measurements of I = 1/2 K{sup -} {pi}{sup +} scattering in the invariant mass range in which scattering is predominantly elastic. If the data are mostly I = 1/2, this observation indicates that the Watson theorem, which requires these phases to have the same dependence on invariant mass, does not apply to these decays. The production rate of K{sup -}{pi}{sup +} from these decays, if assumed to be predominantly I = 1/2, is also found to have a significant dependence on invariant mass in the region above 1.25 GeV/c{sup 2}. These measurements can provide a relatively model-free basis for future attempts to determine which strange scalar amplitudes contribute to the decays.