We report measurements of isospin asymmetry $\Delta_{0-}$ and difference of direct $CP$ asymmetries $\Delta A_{CP}$ between charged and neutral $B \to X_s \gamma$ decays. This analysis is based on ...the data sample containing $772 \times 10^6 B\bar{B}$ pairs that was collected with the Belle detector at the KEKB energy-asymmetric $e^+ e^-$ collider. Using a sum-of-exclusive technique with invariant $X_s$ mass up to 2.8~GeV/$c^2$, we obtain $\Delta_{0-} = \bigl-0.48 \pm 1.49 {\rm (stat.)} \pm 0.97 {\rm (syst.)} \pm 1.15 {(f_{+-}/f_{00})}\bigr$\% and $\Delta A_{CP} = \bigl+3.69 \pm 2.65 {\rm (stat.)} \pm 0.76{\rm (syst.)}\bigr$\%, where the last uncertainty for $\Delta_{0-}$ is due to the uncertainty on the production ratio of $B^+B^-$ to $B^0\bar{B}^0$ in $\Upsilon(4S)$ decays. The measured value of $\Delta_{0-}$ is consistent with zero, allowing us to constrain the resolved photon contribution in the $B \to X_s \gamma$, and improve the branching fraction prediction. The result for $\Delta A_{CP}$ is consistent with the prediction of the SM. We also measure the direct $CP$ asymmetries for charged and neutral $B \to X_s \gamma$ decays. All the measurements are the most precise to date.
We study charmless hadronic decays of charged B mesons to the final states $K_{S}^{0}K_{S}^{0}K^±$ and $K_{S}^{0}K_{S}^{0}π^±$ using a 711 fb$^{-1}$ data sample that contains 772×10$^6$ $B\bar{B}$ ...pairs and was collected at the $ϒ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. For $B^± → K_{S}^{0}K_{S}^{0}K^±$, the measured branching fraction and direct CP asymmetry are $10.42±0.43(stat)±0.22(syst) × 10^{-6 }$ and $+1.6±3.9(stat)±0.9(syst)\%$, respectively. In the absence of a statistically significant signal for $B^± → K_{S}^{0}K_{S}^{0}K^±$, we obtain a 90% confidence-level upper limit on its branching fraction as $8.7 × 10^{-7}$.
Using data samples of $e^+e^-$ collisions collected at the $\Upsilon(1S)$, $\Upsilon(2S)$, and $\Upsilon(3S)$ resonances with the Belle detector, we search for the three-body decay of the ...$\Omega(2012)$ baryon to $K\pi\Xi$. This decay is predicted to dominate for models describing the $\Omega(2012)$ as a $K\Xi(1530)$ molecule. No significant $\Omega(2012)$ signals are observed in the studied channels, and 90\% credibility level upper limits on the ratios of the branching fractions relative to $K \Xi$ decay modes are obtained.
We report a measurement of time-dependent $CP$ violation in $B^0 \to K^0_S \pi^0 \pi^0$ decays using a data sample of $772 \times 10^6$ $B\bar{B}$ pairs collected by the Belle experiment runnin g at ...the $\Upsilon (4S)$ resonance at the KEKB $e^+ e^-$ collider. This decay proceeds mainly via a $b\to sd\bar{d}$ 'penguin' amplitude. The results are $\sin 2\phi^{\rm eff}_1 = 0.92^{+0.27}_{-0.31}~$ (stat.) $\pm 0.11$ (syst.) and $\mathcal{A} = 0.28 \pm 0.21$ (stat.) $\pm 0.04$ (syst.), which are the most precise measurements of $CP$ violati on in this decay mode to date. The value for the $CP$-violating parameter $\sin 2\phi^{\rm eff}_1$ is consistent with that obtained using decay modes proceeding via a $b\to c\bar{c}s$ 'tree' amplitude.
This work reports the first observation of azimuthal asymmetries around the thrust axis in e+e− annihilation of pairs of back-to-back charged pions in one hemisphere, and π0 and η mesons in the ...opposite hemisphere. These results are complemented by a new analysis of pairs of back-to-back charged pions. The π0 and η asymmetries rise with the relative momentum z of the detected hadrons as well as with the transverse momentum with respect to the thrust axis. These asymmetries are sensitive to the Collins fragmentation function H⊥1 and provide complementary information to previous measurements with charged pions and kaons in the final state. In particular, the η final states will provide additional information on the flavor structure of H⊥1. This is the first measurement of the explicit transverse-momentum dependence of the Collins fragmentation function from Belle data. It uses a dataset of 980.4 fb−1 collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV.
We report the study of $B^{+} \rightarrow p\bar{\Lambda} K^+ K^-$ and $B^{+} \rightarrow \bar{p}\Lambda K^+ K^+$ using a $772 \times 10^6$ $B\bar{B}$ pair data sample recorded on the $\Upsilon({\rm ...4S})$ resonance with the Belle detector at KEKB. These include the observations of decay modes with the corresponding branching fractions $\mathcal{B}$($B^{+} \rightarrow p\bar{\Lambda} K^+ K^-$ ) $=$ $(4.22^{+0.45}_{-0.44}\pm 0.51)\times10^{-6}$, $\mathcal{B}$($B^{+} \rightarrow \bar{p}\Lambda K^+ K^+$) $=$ $(3.81^{+0.39}_{-0.37} \pm 0.45)\times 10^{-6}$, $\mathcal{B}$($\eta_c \rightarrow p \bar{\Lambda} K^-$) $=$ $(2.9^{+0.4}_{-0.3}\pm 0.4)\times10^{-3}$ and $\mathcal{B}$($B^{+} \rightarrow p\bar{\Lambda} \phi$) $=$ $(0.818 \pm 0.215 \pm 0.078)\times10^{-6}$, where $\mathcal{B}$ denotes the decay branching fraction and the intermediate resonance decays are excluded in the four-body decay measurements.
We present the first measurements of branching fractions of rare tau-lepton decays, τ-→π-ντℓ+ℓ- (ℓ=e or μ), using a data sample corresponding to 562 fb-1 collected at a center-of-mass energy of 10.58 ...GeV with the Belle detector at the KEKB asymmetric-energy e+e- collider. The τ-→π-ντe+e- decay is observed for the first time with 7.0σ significance. The partial branching fraction determined by the structure-dependent mechanisms mediated by either a vector or an axial-vector current for the mass region Mπee>1.05 GeV/c2 is measured to be B(τ-→π-ντe+e-)Mπ-e+e->1.05 GeV/c2=(5.90±0.53±0.85±0.11)×10-6, where the first uncertainty is statistical, the second is systematic, and the third is due to model dependence. In the full phase space, due to the different detection efficiencies for the structure-dependent mechanisms mediated by axial-vector and vector currents, the branching fraction varies from BA(τ-→π-ντe+e-)=(1.46±0.13±0.21)×10-5 to BV(τ-→π-ντe+e-)=(3.01±0.27±0.43)×10-5, respectively. An upper limit is set on the branching fraction of the τ-→π-ντμ+μ- decay, B(τ-→π-ντμ+μ-)<1.14×10-5, at the 90% confidence level.
We present the first model-independent measurement of the CKM unitarity triangle angle ϕ3 using B±→ D(K0Sπ+π−π0) K± decays, where D indicates either a D0 or D¯¯¯¯0 meson. Measurements of the ...strong-phase difference of the D →K0Sπ+π−π0 amplitude obtained from CLEO-c data are used as input. This analysis is based on the full Belle data set of 772 × 106BB¯¯¯¯ events collected at the Υ(4S) resonance. We obtain ϕ3 = (5.7+10.2−8.8±3.5±5.7)° and the suppressed amplitude ratio rB = 0.323±0.147±0.023±0.051. Here the first uncertainty is statistical, the second is the experimental systematic, and the third is due to the precision of the strong-phase parameters measured from CLEO-c data. The 95% confidence interval on ϕ3 is (−29.7, 109.5)°, which is consistent with the current world average.
We report the results of a search for the decay $B^0 → X(3872)(→ J/ψ π^+ π^−)γ$. The analysis is performed on a data sample corresponding to an integrated luminosity of 711fb$^{−1}$ and containing ...$772 \times 10^6 B\bar{B}$ pairs, collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^−$ collider running at the $Υ(4S)$ resonance energy. We find no evidence for a signal and place an upper limit of $\mathcal{B}(B^0 → X(3872)γ) \times \mathcal{B}(X(3872) → J/ψ π^+ π^−) < 5.1 \times 10^{−7}$ at 90% confidence level.
We report on the first Belle search for a light CP-odd Higgs boson, $A^{0}$, that decays into low mass dark matter, $\chi$, in final states with a single photon and missing energy. We search for ...events produced via the dipion transition $\Upsilon(\textrm{2S})\rightarrow\Upsilon(\textrm{1S})\pi^{+}\pi^{-}$, followed by the on-shell process $\Upsilon(\textrm{1S})\rightarrow\gamma A^{0}$ with $A^{0} \rightarrow\chi\chi$, or by the off-shell process $\Upsilon(\textrm{1S})\rightarrow\gamma\chi\chi$. Utilizing a data sample of 157.3 $\times$ 10$^{6}$ $\Upsilon(\textrm{2S})$ decays, we find no evidence for a signal. We set limits on the branching fractions of such processes in the mass ranges below 5 $GeV/c^2$
