We report a search for charmless hadronic decays of neutral \(B\) mesons to \(\eta' K^{*}(892)^{0}\). The results are based on a 711fb\(^{-1}\) data sample that contains \(772\times 10^6 ...B\overline{B}\) pairs, collected at the \(\Upsilon(4S)\) resonance with the Belle detector at the KEKB asymmetric energy \(e^+e^-\) collider. We observe the decay for the first time with a significance of 5.0 standard deviations and obtain its branching fraction \({\cal B}B^0\to\eta' K^{*}(892)^{0}=2.6\pm0.7{\rm (stat)}\pm0.2{\rm (syst)}\times 10^{-6}\). We also measure the \(CP\) violating asymmetry as \({\cal A}_{CP}B^0\to\eta' K^{*}(892)^{0}=-0.22\pm0.29{\rm (stat)}\pm0.07{\rm syst}\).
We search for the decay \(B_{s}^{0}\rightarrow\gamma\gamma\) and measure the branching fraction for \(B_{s}^{0}\rightarrow\phi\gamma\) using 121.4~\(\textrm{fb}^{-1}\) of data collected at the ...\(\Upsilon(\mathrm{5}S)\) resonance with the Belle detector at the KEKB asymmetric-energy \(e^{+}e^{-}\) collider. The \(B_{s}^{0}\rightarrow\phi\gamma\) branching fraction is measured to be \((3.6 \pm 0.5 (\mathrm{stat.}) \pm 0.3 (\mathrm{syst.}) \pm 0.6 (f_{s})) \times 10^{-5}\), where \(f_{s}\) is the fraction of \(B_{s}^{(*)}\bar{B}_{s}^{(*)}\) in \(b\bar{b}\) events. Our result is in good agreement with the theoretical predictions as well as with a recent measurement from LHCb. We observe no statistically significant signal for the decay \(B_{s}^{0}\rightarrow\gamma\gamma\) and set a \(90\%\) confidence-level upper limit on its branching fraction at \( 3.1 \times 10^{-6}\). This constitutes a significant improvement over the previous result.
We report a measurement of the \(B^0\) and \(B^+\) meson decays to the \(D_s^-K^0_S \pi^+\) and \(D_s^- K^+K^+\) final states, respectively, using \(657 \times 10^{6} B\overline{B}\) pairs collected ...at the \(\Upsilon(4S)\) resonance with the Belle detector at the KEKB asymmetric-energy \(e^+e^-\) collider. Using the \(D_s^-\to \phi\pi^-\), \(K^{*}(892)^0 K^-\) and \(K^0_S K^-\) decay modes for the \(D_s\) reconstruction, we measure the following branching fractions: \({\cal B}(B^0\to D_s^{-}K^0_S\pi^+)=0.47 \pm 0.06 (\mathrm {stat}) \pm 0.05 (\mathrm {syst})\times 10^{-4}\) and \({\cal B}(B^+\to D_s^-K^+K^+)= 0.93 \pm 0.22 (\mathrm {stat})\pm 0.10 (\mathrm {syst})\times 10^{-5}\). We find the ratio of the branching fraction of \(B^+\to D_s^-K^+K^+\) to that of the analogous Cabibbo favored \(B^+\to D_s^-K^+\pi^+\) decay to be \({\cal R}_{\cal B} = 0.054 \pm 0.013 ({\rm stat}) \pm 0.006 ({\rm syst})\), which is consistent with the na\"ıve factorization model. We also observe a deviation from the three-body phase-space model for both studied decays.
We report a measurement of \({D^{0}}\)-\({\overline{D}{}^{0}}\) mixing parameters and a search for indirect \(CP\) violation through a time-dependent amplitude analysis of \({D^0\to ...K_S^0\pi^+\pi^-}\) decays. The results are based on 921~fb\(^{-1}\) of data accumulated with the Belle detector at the KEKB asymmetric-energy \(e^+e^-\) collider. Assuming \(CP\) conservation, we measure the mixing parameters \(x=(0.56\pm0.19^{+0.03}_{-0.09}{^{+0.06}_{-0.09}})\%\) and \(y=(0.30\pm0.15^{+0.04}_{-0.05}{^{+0.03}_{-0.06})}\%\), where the errors are statistical, experimental systematic, and systematic due to the amplitude model, respectively. With \(CP\) violation allowed, the parameters \(|q/p|=0.90^{+0.16}_{-0.15}{^{+0.05}_{-0.04}}{^{+0.06}_{-0.05}}\) and \(\arg(q/p)=(-6\pm11{\pm3}{^{+3}_{-4}})^{\circ}\) are found to be consistent with conservation of \(CP\) symmetry in mixing and in the interference between mixing and decay, respectively.
We report the results of a search for the \(X(1835)\) state in the process \(e^+e^-\to J/\psi+X(1835)\) using a data sample of 672 fb\(^{-1}\) collected with the Belle detector at and near the ...\(\Upsilon(4S)\) resonance at the KEKB asymmetric-energy \(e^+e^-\) collider. No significant evidence is found for this process, and an upper limit is set on its cross section times the branching fraction: \(\sigma_{\rm Born}(e^+e^- \to J/\psi X(1835)) \cdot\) {\({\cal B}(X(1835)\to \ge 3\) charged tracks)} \(< 1.3 \ {\rm fb}\) at 90% confidence level.
We report measurements of branching fractions of \(\tau\) lepton decays to final states with a \(K^{0}_{S}\) meson using a 669 fb\(^{-1}\) data sample accumulated with the Belle detector at the KEKB ...asymmetric-energy \(e^{+}e^{-}\) collider. The inclusive branching fraction is measured to be \(\mathcal{B}(\tau^{-} \to K^{0}_{S}\ X^{-} \nu_{\tau})=(9.15 \pm 0.01 \pm 0.15) \times 10^{-3}\), where \(X^{-}\) can be anything; the exclusive branching fractions are \(\mathcal{B}(\tau^{-} \to \pi^{-} K^{0}_{S} \nu_{\tau}) = (4.16 \pm 0.01 \pm 0.08) \times 10^{-3}\), \(\mathcal{B}(\tau^{-} \to K^{-} K^{0}_{S} \nu_{\tau}) = (7.40 \pm 0.07 \pm 0.27) \times 10^{-4}\), \(\mathcal{B}(\tau^{-} \to \pi^{-} K^{0}_{S} \pi^{0} \nu_{\tau}) = (1.93 \pm 0.02 \pm 0.07) \times 10^{-3}\), \(\mathcal{B}(\tau^{-} \to K^{-} K^{0}_{S} \pi^{0} \nu_{\tau}) = (7.48 \pm 0.10 \pm 0.37)\times 10^{-4}\), \(\mathcal{B}(\tau^{-} \to \pi^{-} K^{0}_{S} K^{0}_{S} \nu_{\tau}) = (2.33 \pm 0.03 \pm 0.09) \times 10^{-4}\), \(\mathcal{B}(\tau^{-} \to \pi^{-} K^{0}_{S} K^{0}_{S} \pi^{0} \nu_{\tau}) = (2.00 \pm 0.22 \pm 0.20) \times 10^{-5}\), where the first uncertainty is statistical and the second is systematic. For each mode, the accuracy is improved over that of pre-\(B\)-factory measurements by a factor ranging from five to ten. In \(\tau^{-} \to \pi^{-} K^0_S K^0_S \pi^{0} \nu_{\tau}\) decays, clear signals for the intermediate states \(\tau^{-} \to \pi^- f_{1}(1285)\nu_{\tau}\) and \(\tau^{-} \to K^{*-}K^{0}_{S} \pi^{0} \nu_{\tau}\) are observed.
We present the result of a direct search for the decay K_S -> e+e-, obtained with a sample of e+e- -> phi -> K_S K_L events produced at DAFNE, the Frascati phi-factory, for an integrated luminosity ...of 1.9 fb^-1. The search has been performed using a pure K_S beam tagged by the simultaneous detection of a K_L interaction in the calorimeter. Background rejection has been optimized by using both kinematic and particle identification cuts. We find BR(K_S -> e+e-) < 9x10^-9 at 90% CL, which improves by an order of magnitude on the previous best limit.
We present measurements of the masses and decay widths of the baryonic states \(\Sigma_{c}(2455)^{0/++}\) and \(\Sigma_{c}(2520)^{0/++}\) using a data sample corresponding to an integrated luminosity ...of 711 fb\(^{-1}\) collected with the Belle detector at the KEKB \(e^{+}e^{-}\) asymmetric-energy collider operating at the \(\Upsilon(4S)\) resonance. We report the mass differences with respect to the \(\Lambda_{c}^{+}\) baryon \(M(\Sigma_{c}(2455)^{0})-M(\Lambda_{c}^{+}) = 167.29\pm0.01\pm0.02\) MeV/\(c^{2}\), \(M(\Sigma_{c}(2455)^{++})-M(\Lambda_{c}^{+}) = 167.51\pm0.01\pm0.02\) MeV/\(c^{2}\), \(M(\Sigma_{c}(2520)^{0})-M(\Lambda_{c}^{+}) = 231.98\pm0.11\pm0.04\) MeV/\(c^{2}\), \(M(\Sigma_{c}(2520)^{++})-M(\Lambda_{c}^{+}) = 231.99\pm0.10\pm0.02\) MeV/\(c^{2}\), and the decay widths \(\Gamma(\Sigma_{c}(2455)^{0}) = 1.76\pm0.04^{+0.09}_{-0.21}\) MeV/\(c^{2}\), \(\Gamma(\Sigma_{c}(2455)^{++}) = 1.84\pm0.04^{+0.07}_{-0.20}\) MeV/\(c^{2}\), \(\Gamma(\Sigma_{c}(2520)^{0}) = 15.41\pm0.41^{+0.20}_{-0.32}\) MeV/\(c^{2}\), \(\Gamma(\Sigma_{c}(2520)^{++}) = 14.77\pm0.25^{+0.18}_{-0.30}\) MeV/\(c^{2}\), where the first uncertainties are statistical and the second are systematic. The isospin mass splittings are measured to be \(M(\Sigma_{c}(2455)^{++})-M(\Sigma_{c}(2455)^{0})=0.22\pm0.01\pm0.01\) MeV/\(c^{2}\) and \(M(\Sigma_{c}(2520)^{++})-M(\Sigma_{c}(2520)^{0})=0.01\pm0.15\pm0.03\) MeV/\(c^{2}\). These results are the most precise to date.
We observe \(D^0-\bar{D}^0\) mixing in the decay \(D^0\rightarrow K^+\pi^-\) using a data sample of integrated luminosity 976 fb\(^{-1}\) collected with the Belle detector at the KEKB \(e^+e^-\) ...asymmetric-energy collider. We measure the mixing parameters \({x'}^2 = (0.09\pm0.22)\times 10^{-3}\) and \(y' = (4.6\pm3.4)\times 10^{-3}\) and the ratio of doubly Cabibbo-suppressed to Cabibbo-favored decay rates \(R_D = (3.53\pm0.13)\times 10^{-3}\), where the uncertainties are statistical and systematic combined. Our measurement excludes the no-mixing hypothesis at the 5.1 standard deviation level.
We report a measurement of the branching fraction of the decay \(B^0_s\to J/\psi\,\phi(1020)\), evidence and a branching fraction measurement for \(B^0_s\to J/\psi\,f'_2(1525)\), and the ...determination of the total \(B^0_s\to J/\psi\,K^+K^-\) branching fraction, including the resonant and non-resonant contributions to the \(K^+K^-\) channel. We also determine the \(S\)-wave contribution within the \(\phi(1020)\) mass region. The absolute branching fractions are \(\mathcal{B}B^0_s\to J/\psi\,\phi(1020)=(1.25 \pm 0.07\left(\mathrm{stat}\right)\pm 0.08\left(\mathrm{syst}\right)\pm 0.22\left(f_s\right))\times 10^{-3}\), \(\mathcal{B}B^0_s\to J/\psi\,f'_2(1525)=(0.26\pm 0.06\left(\mathrm{stat}\right)\pm 0.02\left(\mathrm{syst}\right) \pm 0.05\left(f_s\right))\times 10^{-3}\) and \(\mathcal{B}B^0_s\to J/\psi\,K^+K^- = (1.01\pm 0.09\left(\mathrm{stat}\right) \pm 0.10\left(\mathrm{syst}\right)\pm 0.18\left(f_s\right))\times 10^{-3}\), where the last systematic error is due to the branching fraction of \(b\bar{b}\to B^{(*)}_s B^{(*)}_s\). The branching fraction ratio is found to be \(\mathcal{B}B^0_s\to J/\psi\,f'_2(1525)/\mathcal{B}B^0_s\to J/\psi\,\phi(1020)=(21.5\pm 4.9\left(\mathrm{stat}\right) \pm2.6\left(\mathrm{syst}\right))%\). All results are based on a 121.4 fb\(^{-1}\) data sample collected at the \(\Upsilon(5S)\) resonance by the Belle experiment at the KEKB asymmetric-energy \(e^+e^-\) collider.
