We study $B\to K^{(*)}{\ell }^{+}{\ell }^{-}$ decays ($\ell =e$, $\mu$) based on a data sample of $657\times {10}^6$ $B\overline{B}$ pairs collected with the Belle detector at the KEKB $e^{+}{e}^{-}$ collider. We report the differential branching fraction, isospin asymmetry, $K^{*}$ polarization, and the forward-backward asymmetry ($A_{\mathrm{FB}}$) as functions of $q^2=M_{\ell \ell }^2{c}^2$. The fitted $A_{\mathrm{FB}}$ spectrum exceeds the standard model expectation by 2.7 standard deviations. The measured branching fractions are $\mathcal{B}(B\to K^{*}{\ell }^{+}{\ell }^{-})=({10.7}_{-1.0}^{+1.1}\pm 0.9)\times {10}^{-7}$ and $\mathcal{B}(B\to K{\ell }^{+}{\ell }^{-})=({4.8}_{-0.4}^{+0.5}\pm 0.3)\times {10}^{-7}$, where the first errors are statistical and the second are systematic, with the muon to electron ratios $R_{K^{*}}=0.83\pm 0.17\pm 0.08$ and $R_K=1.03\pm 0.19\pm 0.06$.

We report a measurement of the exclusive $e^{+}{e}^{-}\to {\Lambda }_c^{+}{\Lambda }_c^{-}$ cross section as a function of center-of-mass energy near the ${\Lambda }_c^{+}{\Lambda }_c^{-}$ threshold. A clear peak with a significance of $8.2\sigma$ is observed in the ${\Lambda }_c^{+}{\Lambda }_c^{-}$ invariant mass distribution just above threshold. With an assumption of a resonance origin for the observed peak, a mass and width of $M=[{4634}_{-7}^{+8}(\mathrm{stat}{)}_{-8}^{+5}(\mathrm{syst})]\mathrm{MeV}/c^2$ and ${\Gamma }_{\mathrm{tot}}=[{92}_{-24}^{+40}(\mathrm{stat}{)}_{-21}^{+10}(\mathrm{syst})]\mathrm{MeV}$ are determined. The analysis is based on a study of events with initial-state-radiation photons in a data sample collected with the Belle detector at the ${\rm Y}(4S)$ resonance and nearby continuum with an integrated luminosity of $695{\mathrm{fb}}^{-1}$ at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.

We report the first observation of two resonancelike structures in the ${\pi }^{+}{\chi }_{c1}$ invariant mass distribution near $4.1\mathrm{GeV}/c^2$ in exclusive ${\overline{B}}^0\to K^{-}{\pi }^{+}{\chi }_{c1}$ decays. From a Dalitz plot analysis in which the ${\pi }^{+}{\chi }_{c1}$ mass structures are represented by Breit-Wigner resonance amplitudes, we determine masses and widths of: $M_1=(4051\pm {14}_{-41}^{+20})\mathrm{MeV}/c^2$, ${\Gamma }_1=({82}_{-17-22}^{+21+47})\mathrm{MeV}$, $M_2=({4248}_{-29-35}^{+44+180})\mathrm{MeV}/c^2$, and ${\Gamma }_2=({177}_{-39-61}^{+54+316})\mathrm{MeV}$; and product branching fractions of $\mathcal{B}({\overline{B}}^0\to K^{-}{Z}_{1,2}^{+})\times \mathcal{B}(Z_{1,2}^{+}\to {\pi }^{+}{\chi }_{c1})=({3.0}_{-0.8-1.6}^{+1.5+3.7})\times {10}^{-5}$ and $({4.0}_{-0.9-0.5}^{+2.3+19.7})\times {10}^{-5}$, respectively. Here the first uncertainty is statistical, the second is systematic. The significance of each of the ${\pi }^{+}{\chi }_{c1}$ structures exceeds $5\sigma$, including the systematic uncertainty from various fit models. This analysis is based on $657\times {10}^6$ $B\overline{B}$ events collected at the ${\rm Y}(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}{e}^{-}$ collider.

The Collins effect connects transverse quark spin with a measurable azimuthal asymmetry in the yield of hadronic fragments around the quark’s momentum vector. Using two different reconstruction methods we measure statistically significant azimuthal asymmetries for charged pion pairs in $e^{+}{e}^{-}$ annihilation at center-of-mass energies of 10.52 GeV and 10.58 GeV, which can be attributed to the fragmentation of primordial quarks with transverse spin components. The measurement was performed using a data set of $547{\mathrm{fb}}^{-1}$ collected by the Belle detector at KEKB improving the statistics of the previously published results by nearly a factor of 20.