Measurement of branching fractions and CP violation parameters in B→ωK decays with first evidence of CP violation in B0→ωKs0

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We present a measurement of the branching fractions and charge-parity-($CP$-)violating parameters in $B\ensuremath{\rightarrow}\ensuremath{\omega}K$ decays. The results are obtained from the final data sample containing $772\ifmmode\times\else\texttimes\fi{}{10}^{6}$ $B\overline{B}$ pairs collected at the $\mathrm{\ensuremath{\Upsilon}}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy ${e}^{+}{e}^{\ensuremath{-}}$ collider. We obtain the branching fractions $\mathcal{B}({B}^{0}\ensuremath{\rightarrow}\ensuremath{\omega}{K}^{0})=(4.5\ifmmode\pm\else\textpm\fi{}0.4(\text{stat})\ifmmode\pm\else\textpm\fi{}0.3(\text{syst}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6},\mathcal{B}({B}^{+}\ensuremath{\rightarrow}\ensuremath{\omega}{K}^{+})=\phantom{\rule{0ex}{0ex}}(6.8\ifmmode\pm\else\textpm\fi{}0.4(\text{stat})\ifmmode\pm\else\textpm\fi{}0.4(\text{syst}))\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}6}$ which are in agreement with their respective current world averages. For the $CP$-violating parameters, we obtain ${\mathcal{A}}_{\ensuremath{\omega}{K}_{S}^{0}}=\ensuremath{-}0.36\ifmmode\pm\else\textpm\fi{}0.19(\text{stat})\ifmmode\pm\else\textpm\fi{}0.05(\text{syst}),{\mathcal{S}}_{\ensuremath{\omega}{K}_{S}^{0}}=+0.91\ifmmode\pm\else\textpm\fi{}0.32(\text{stat})\ifmmode\pm\else\textpm\fi{}0.05(\text{syst}),{\mathcal{A}}_{\ensuremath{\omega}{K}^{+}}=\ensuremath{-}0.03\ifmmode\pm\else\textpm\fi{}0.04(\text{stat})\ifmmode\pm\else\textpm\fi{}0.01(\text{syst}),$ where $\mathcal{A}$ and $\mathcal{S}$ represent the direct and mixing-induced $CP$ asymmetry, respectively. We find no evidence of $CP$ violation in the decay channel ${B}^{+}\ensuremath{\rightarrow}\ensuremath{\omega}{K}^{+}$; however, we obtain the first evidence of $CP$ violation in the ${B}^{0}\ensuremath{\rightarrow}\ensuremath{\omega}{K}_{S}^{0}$ decay channel at the level of 3.1 standard deviations.

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