Abstract
The processes $\gamma \gamma \rightarrow K ^0 _S K ^{\pm} \pi ^{\mp}$ and $\gamma \gamma \rightarrow K ^+ K ^- \pi ^0$ are studied using a data sample of $519$ fb$^{-1}$ recorded with the \babar detector operating at the SLAC PEP-II asymmetric-energy $e^+ e^-$ collider at center of massenergies at and near the $\Upsilon$(n $=$ 2, 3, 4) resonances. In both final states we observe $\eta _c$ decays and Dalitz plot analyses are performed using a model-independent partial wave technique. This allows a model-independent measurement of the mass-dependence of the $I= \frac {1}{2}$ K$\pi$ S-wave amplitude and phase. This measurement is compared to those from previous experiments and the phase shows similar behavior for up to a mass of 1.5 GeV/c$^2$ but the amplitudes exhibit very marked differences. The presence of a new a$_0$(1950) resonance is required by the data with $m=1931 \pm 14 \pm 22$ MeV/c$^2$ and $\Gamma = 271 \pm 22 \pm 29$ MeV.
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