Evidence for $CP$ violation in $B^{+}\to K^{\ast }(892{)}^{+}{\pi }^0$ from a Dalitz plot analysis of $B^{+}\to K_{\mathrm{S}}^0{\pi }^{+}{\pi }^0$ decays

Abstract

We report a Dalitz plot analysis of charmless hadronic decays of charged $B$ mesons to the final state $K_{\mathrm{S}}^0{\pi }^{+}{\pi }^0$ using the full BaBar dataset of $470.9\pm 2.8$ million $B\bar{B}$ events collected at the ${\rm Y}(4S)$ resonance. We measure the overall branching fraction and $CP$ asymmetry to be $\mathcal{B}\left(B^{+}\to K^0{\pi }^{+}{\pi }^0\right)=\left(45.9\pm 2.6\pm 3.0_{-0.0}^{+8.6}\right)\times 10^{-6}$ and $A_{CP}\left(B^{+}\to K^0{\pi }^{+}{\pi }^0\right)=0.07\pm 0.05\pm 0.03_{-0.03}^{+0.02}$, where the uncertainties are statistical, systematic, and due to the signal model, respectively. This is the first measurement of the branching fraction for $B^{+}\to K^0{\pi }^{+}{\pi }^0$. We find first evidence of a $CP$ asymmetry in $B^{+}\to K^{\ast }(892{)}^{+}{\pi }^0$ decays: $A_{CP}\left(B^{+}\to K^{\ast }(892{)}^{+}{\pi }^0\right)=-0.52\pm 0.14\pm 0.04_{-0.02}^{+0.04}$. The significance of this asymmetry, including systematic and model uncertainties, is $3.4$ standard deviations. We also measure the branching fractions and $CP$ asymmetries for three other intermediate decay modes.

22 pages, 15 postscript figures

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