Dalitz plot analysis of three-body Charmonium Decays at BaBar

We present preliminary results on the measurement of the I=1/2 $K \pi$ $\mathcal{S}$-wave through a model independent partial wave analysis of $\eta_c$ decays to $K^0_S K^+ \pi^-$ and $K^+ K^- \pi^0$ produced in two-photon interactions. We also perform a Dalitz plot analysis of the $J/\psi$ decays to $\pi^+ \pi^- \pi^0$ and $K^+ K^- \pi^0$ produced by the initial state radiation process.