Improved measurements of branching fractions and $CP$ partial rate asymmetries for $B\to \omega K$ and $B\to \omega \pi$

We report improved measurements of $B$ to pseudoscalar-vector decays containing an $\omega$ meson in the final state. Our results are obtained from a data sample that contains $388\times {10}^6$ $B\overline{B}$ pairs accumulated at the ${\rm Y}(4S)$ resonance, with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider. We measure the following branching fractions: $\mathcal{B}(B^{+}\to \omega K^{+})=[8.1\pm 0.6(\mathrm{stat}.)\pm 0.6(\mathrm{syst}.)]\times {10}^{-6}$, $\mathcal{B}(B^{+}\to \omega {\pi }^{+})=[6.9\pm 0.6(\mathrm{stat}.)\pm 0.5(\mathrm{syst}.)]\times {10}^{-6}$, and $\mathcal{B}(B^0\to \omega K^0)=[{4.4}_{-0.7}^{+0.8}(\mathrm{stat}.)\pm 0.4(\mathrm{syst}.)]\times {10}^{-6}$. The partial width ratio $\frac{\Gamma (B^{+}\to \omega K^{+})}{\Gamma (B^0\to \omega K^0)}=1.7\pm 0.3(\mathrm{stat}.)\pm 0.1(\mathrm{sys}.)$. We also set the 90% confidence level upper limit $\mathcal{B}(B^0\to \omega {\pi }^0)<2.0\times {10}^{-6}$. In addition, we obtain the partial rate asymmetries ${\mathcal{A}}_{CP}={0.05}_{-0.07}^{+0.08}(\mathrm{stat}.)\pm 0.01(\mathrm{syst}.)$ for $B^{+}\to \omega K^{+}$, and ${\mathcal{A}}_{CP}=-0.02\pm 0.09(\mathrm{stat}.)\pm 0.01(\mathrm{syst}.)$ for $B^{+}\to \omega {\pi }^{+}$.

Figure 1

Projections of fit results on $M_{\mathrm{bc}}$ (within the region of $|\Delta E|\le 0.1\mathrm{GeV}$, $-0.15\mathrm{GeV}\le \Delta E\le 0.1\mathrm{GeV}$ for $\omega {\pi }^0$) and $\Delta E$ (within the region of $5.27\mathrm{GeV}/c^2<M_{\mathrm{bc}}<5.29\mathrm{GeV}/c^2$) for $\omega K^{+}$, $\omega {\pi }^{+}$, $\omega K^0$, and $\omega {\pi }^0$. Open histograms are data, solid curves are the fit functions, solid-dotted lines represent the signals, dashed lines show the sum of $q\overline{q}$ continuum and $b\to c$, dotted lines are due to other charmless $B$ decays, and cross-hatched areas represent reflections due to $K\mathrm{\text{−}}\pi$ misidentification.

Figure 2

Background-subtracted one-dimentional projections are obtained from data fit results in bins of fit yields in (left) the invariant mass ${\mathcal{M}}_{\omega \to {\pi }^{+}{\pi }^{-}{\pi }^0}$ and (right) the absolute value of the cosine of the helicity angle $|\cos {\theta }_{\mathrm{hel}}^{\omega }|$ for $\omega K^{+}$, $\omega {\pi }^{+}$, and $\omega K^0$ candidate events. Points are data, and histograms are from MC expectations for $B\to \omega h$.