Dalitz plot analysis of $η_c \to K^+ K^- η$ and $η_c \to K^+ K^- π^0$ in two-photon interactions

We study the processes $γγ\to K^+ K^- η$ and $γγ\to K^+ K^- π^0$ 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-mass energies at and near the $Υ(nS)$ ($n = 2,3,4$) resonances. We observe $η_c \to K^+ K^- η$ and $η_c \to K^+ K^- π^0$ decays, measure their relative branching fraction, and perform a Dalitz plot analysis for each decay. We observe the $K^*_0(1430) \to K η$ decay and measure its branching fraction relative to the $K π$ decay mode to be ${\cal R}(K^*_0(1430)) = \frac{{\cal B}(K^*_0(1430) \to K η)}{{\cal B}(K^*_0(1430) \to K π)} = 0.092 \pm 0.025^{+0.010}_{-0.025}$. The $η_c \to K^+ K^- η$ and $K^*_0(1430) \to K η$ results correspond to the first observations of these channels. The data also show evidence for $η_c(2S) \to K^+ K^- π^0$ and first evidence for $η_c(2S) \to K^+ K^- η$.

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