arXiv subjects

H. Miyata

Publications and source records attributed to H. Miyata.

At least 19 recordsLinked to original sources

arXiv2020

Test of lepton-flavor universality in ${B\to K^\ast\ell^+\ell^-}$ decays at Belle

We present a measurement of $R_{K^{\ast}}$, the branching fraction ratio ${{\cal B}(B\to K^\ast μ^+ μ^-)}$/ ${{\cal B}(B\to K^\ast e^+ e^-)}$, for both charged and neutral $B$ mesons. The ratio for the charged case, $R_{K{^{\ast +}}}$, is the first measurement ever performed. In addition, we report absolute branching fractions for the individual modes in bins of the squared dilepton invariant mass, $q^2$. The analysis is based on a data sample of $711~\mathrm{fb}^{-1}$, containing $772\times 10^{6}$ $B\bar B$ events, recorded at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The obtained results are consistent with Standard Model expectations.

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arXiv2019

Measurements of the Branching Fractions ${\cal B}(B^{-} \to \barΛ_{c}^{-} Ξ_{c}^{'0})$, ${\cal B}(B^{-} \to \barΛ_{c}^{-} Ξ_{c}(2645)^{0})$ and ${\cal B}(B^{-} \to \barΛ_{c}^{-} Ξ_{c}(2790)^{0}) $

Using the data sample of 711 fb$^{-1}$ of $Υ(4S)$ on-resonance data taken by the Belle detector at the KEKB asymmetric-energy electron-positron collider, we present the first measurements of branching fractions of the decays $B^{-} \to \barΛ_{c}^{-} Ξ_{c}^{'0}$, $B^{-} \to \barΛ_{c}^{-} Ξ_{c}(2645)^{0}$, and $B^{-} \to \barΛ_{c}^{-} Ξ_{c}(2790)^{0} $. The signal yields for these decays are extracted from the recoil mass spectrum of the system recoiling against $\barΛ_{c}^{-}$ baryons in selected $B^-$ candidates. The branching fraction of $B^{-} \to \barΛ_{c}^{-} Ξ_{c}(2790)^{0}$ is measured to be $ (1.1 \pm 0.4 \pm 0.2)\times 10^{-3}$, where the first uncertainty is statistical and the second systematic. The 90\% credibility level upper limits on ${\cal B}(B^{-} \to \barΛ_{c}^{-} Ξ_{c}^{'0})$ and ${\cal B}(B^{-} \to \barΛ_{c}^{-} Ξ_{c}(2645)^{0})$ are determined to be $6.5\times 10^{-4}$ and $7.9\times 10^{-4}$, respectively.

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arXiv2019

Observation of a vector charmoniumlike state in $e^+e^- \to D^+_sD_{s1}(2536)^-+c.c.$

Using a data sample of 921.9 fb$^{-1}$ collected with the Belle detector, we study the process of $e^+e^-\to D^+_sD_{s1}(2536)^-+c.c.$ via initial-state radiation. We report the first observation of a vector charmoniumlike state decaying to $D^+_sD_{s1}(2536)^-+c.c.$ with a significance of 5.9$σ$, including the systematic uncertainties. The measured mass and width are $(4625.9^{+6.2}_{-6.0}({\rm stat.})\pm0.4({\rm syst.}))~{\rm MeV}/c^{2}$ and $(49.8^{+13.9}_{-11.5}({\rm stat.})\pm4.0({\rm syst.}))~{\rm MeV}$, respectively. The product of the $e^+e^-\to D^+_sD_{s1}(2536)^-+c.c.$ cross section and the branching fraction of $D_{s1}(2536)^-\to{\bar D}^{*0}K^-$ is measured from the $D_s \bar{D}_{s1}(2536)$ threshold to 5.59~GeV.

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arXiv2019

Observation of the radiative decays of $Υ(1S)$ to $χ_{c1}$

We report the first observation of the radiative decay of the $Υ(1S)$ into a charmonium state. The statistical significance of the observed signal of $Υ(1S) \to γχ_{c1}$ is 6.3 standard deviations including systematics. The branching fraction is calculated to be Br($Υ(1S) \to γχ_{c1}$) = (4.7^{+2.4}_{-1.8} (stat) ^{+0.4}_{-0.5} (sys)) * 10^{-5}. We also searched for $Υ(1S)$ radiative decays into $χ_{c0,2}$ and $η_c(1S,2S)$ and set upper limits on their branching fractions. These results are obtained from a 24.9 fb^{-1} data sample collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider at a center-of-mass energy equal to the $Υ(2S)$ mass using $Υ(1S)$ tagging by the $Υ(2S) \to Υ(1S) π^+π^-$ transitions.

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arXiv2019

Observation of a new structure near 10.75 GeV in the energy dependence of the $e^+e^-\toΥ(nS)π^+π^-$ ($n=1,2,3$) cross sections

We report a new measurement of the $e^+e^-\toΥ(nS)π^+π^-$ ($n=1,2,3$) cross sections at energies from 10.52 to 11.02 GeV using data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We observe a new structure in the energy dependence of the cross sections; if described by a Breit-Wigner function its mass and width are found to be $M=(10752.7\pm5.9\,^{+0.7}_{-1.1})\,$MeV/$c^2$ and $Γ=(35.5^{+17.6}_{-11.3}\,^{+3.9}_{-3.3})\,$MeV, where the first error is statistical and the second is systematic. The global significance of the new structure including systematic uncertainty is 5.2 standard deviations. We also find evidence for the $e^+e^-\toΥ(1S)π^+π^-$ process at the energy 10.52 GeV, which is below the $B\bar{B}$ threshold.

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arXiv2019

Azimuthal asymmetries of back-to-back $π^\pm-(π^0,η,π^\pm)$ pairs in $e^+e^-$ annihilation

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 $π^0$ and $η$ mesons in the opposite hemisphere. These results are complemented by a new analysis of pairs of back-to-back charged pions. The $π^0$ 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 $H_1^{\perp}$ 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 $H_1^{\perp}$. 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.

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arXiv2019

Search for the $B \to Y(4260) K, ~Y(4260) \to J/ψπ^+π^-$ decays

We report the results of a search for the $B \to Y(4260) K, ~Y(4260)\to J/ψπ^+π^-$ decays. This study is based on a data sample corresponding to an integrated luminosity of 711~fb$^{-1}$, collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We investigate the $J/ψπ^+π^-$ invariant mass distribution in the range 4.0 to 4.6 GeV/$c^2$ using both $B^+ \to J/ψπ^+π^- K^+$ and $B^0 \to J/ψπ^+π^- K^0_S$ decays. We find excesses of events above the background levels, with a significances of 2.1 and 0.9 standard deviations for charged and neutral $B \to Y(4260) K$ decays, respectively, taking into account the systematic uncertainties. These correspond to upper limits on the product of branching fractions, ${\cal B}(B^+ \to Y(4260) K^+) \times {\cal B}(Y(4260) \to J/ψπ^+ π^-) <1.4 \times 10^{-5}$ and ${\cal B}(B^0 \to Y(4260) K^0) \times {\cal B}(Y(4260) \to J/ψπ^+ π^-) <1.7 \times 10^{-5}$ at the 90\% confidence level.

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arXiv2019

First measurements of absolute branching fractions of $Ξ_c^0$ at Belle

We present the first measurements of absolute branching fractions of $Ξ_c^0$ decays into $Ξ^- π^+$, $ΛK^- π^+$, and $p K^- K^- π^+$ final states. The measurements are made using a data set comprising $(772\pm 11)\times 10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. We first measure the absolute branching fraction for $B^- \to \barΛ_c^- Ξ_c^0$ using a missing-mass technique; the result is ${\cal B}(B^- \to \barΛ_c^- Ξ_c^0) = (9.51 \pm 2.10 \pm 0.88) \times 10^{-4}$. We subsequently measure the product branching fractions ${\cal B}(B^- \to \barΛ_c^- Ξ_c^0){\cal B}(Ξ_c^0 \to Ξ^- π^+)$, ${\cal B}( B^- \to \barΛ_c^- Ξ_c^0) {\cal B}(Ξ_c^0 \to ΛK^- π^+)$, and ${\cal B}( B^- \to \barΛ_c^- Ξ_c^0) {\cal B}(Ξ_c^0 \to p K^- K^- π^+)$ with improved precision. Dividing these product branching fractions by the result for $B^- \to \barΛ_c^- Ξ_c^0$ yields the following branching fractions: ${\cal B}(Ξ_c^0 \to Ξ^- π^+)= (1.80 \pm 0.50 \pm 0.14)\%$, ${\cal B}(Ξ_c^0 \to ΛK^- π^+)=(1.17 \pm 0.37 \pm 0.09)\%$, and ${\cal B}(Ξ_c^0 \to p K^- K^- π^+)=(0.58 \pm 0.23 \pm 0.05)\%.$ For the above branching fractions, the first uncertainties are statistical and the second are systematic. Our result for ${\cal B}(Ξ_c^0 \to Ξ^- π^+)$ can be combined with $Ξ_c^0$ branching fractions measured relative to $Ξ_c^0 \to Ξ^- π^+$ to yield other absolute $Ξ_c^0$ branching fractions.

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arXiv2019

Measurement of time-dependent $CP$ violation in $B^0 \to K^0_S π^0 π^0$ decays

We report a measurement of time-dependent $CP$ violation in $B^0 \to K^0_S π^0 π^0$ decays using a data sample of $772 \times 10^6$ $B\bar{B}$ pairs collected by the Belle experiment runnin g at the $Υ(4S)$ resonance at the KEKB $e^+ e^-$ collider. This decay proceeds mainly via a $b\to sd\bar{d}$ "penguin" amplitude. The results are $\sin 2ϕ^{\rm eff}_1 = 0.92^{+0.27}_{-0.31}~$ (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 $\sin 2ϕ^{\rm eff}_1$ is consistent with that obtained using decay modes proceeding via a $b\to c\bar{c}s$ "tree" amplitude.

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arXiv2018

Measurement of the branching fraction and time-dependent $CP$ asymmetry for $B^0\to J/ψπ^0$ decays

We measure the branching fraction and time-dependent $CP$-violating asymmetry for $B^0\to J/ψπ^0$ decays using a data sample of 711 ${\rm fb^{-1}}$ collected on the $Υ(4S)$ resonance by the Belle experiment running at the KEKB $e^+e^-$ collider. The branching fraction is measured to be $\mathcal{B}(B^0\to J/ψπ^0) = [1.62\,\pm 0.11~({\rm stat}) \pm0.07~({\rm syst})]\times 10^{-5}$, which is the most precise measurement to date. The measured $CP$ asymmetry parameters are $\mathcal{S} = -0.59\,\pm 0.19~({\rm stat}) \pm 0.03~({\rm syst})$ and $\mathcal{A} = -0.15\,\pm 0.14~({\rm stat})\,^{+0.04}_{-0.03}~({\rm syst})$. The mixing-induced $CP$ asymmetry ($\mathcal{S}$) differs from the case of no $CP$ violation by 3.0 standard deviations, and the direct $CP$ asymmetry ($\mathcal{A}$) is consistent with zero.

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arXiv2018

Evidence of a structure in $\bar{K}^{0} Λ_{c}^{+}$ consistent with a charged $Ξ_c(2930)^{+}$, and updated measurement of $\bar{B}^{0} \to \bar{K}^{0} Λ_{c}^{+} \barΛ_{c}^{-}$ at Belle

We report evidence for the charged charmed-strange baryon $Ξ_{c}(2930)^+$ with a signal significance of 3.9$σ$ with systematic errors included. The charged $Ξ_{c}(2930)^+$ is found in its decay to $K_{S}^{0} Λ_{c}^+$ in the substructure of $\bar{B}^{0} \to K^{0}_{S} Λ_{c}^{+} \barΛ_{c}^{-}$ decays. The measured mass and width are $[2942.3 \pm 4.4 (\rm stat.) \pm 1.5(\rm syst.)]$~MeV/$c^{2}$ and $[14.8 \pm 8.8(\rm stat.) \pm 2.5(\rm syst.)]$~MeV, respectively, and the product branching fraction is $\cal{B}(\bar{B}^{0} \to Ξ_c(2930)^{+} \barΛ_{c}^{-}) \cal{B}(Ξ_c(2930)^{+}\to \bar{K}^{0} Λ_{c}^{+})=[2.37 \pm 0.51 (\rm stat.)\pm 0.31(\rm syst.)]\times 10^{-4}$. We also measure $\cal{B}(\bar{B}^{0} \to \bar{K}^{0} Λ_{c}^{+} \barΛ_{c}^{-}) = [3.99 \pm 0.76(\rm stat.) \pm 0.51(\rm syst.)] \times 10^{-4}$ with greater precision than previous experiments, and present the results of a search for the charmonium-like state $Y(4660)$ and its spin partner, $Y_η$, in the $Λ_{c}^{+}\barΛ_{c}^{-}$ invariant mass spectrum. No clear signals of the $Y(4660)$ or $Y_η$ are observed and the 90\% credibility level (C.L.) upper limits on their production rates are determined. These measurements are obtained from a sample of $(772\pm11)\times 10^{6} B\bar{B}$ pairs collected at the $Υ(4S)$ resonance by the Belle detector at the KEKB asymmetric energy electron-positron collider.

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arXiv2018

Measurement of eta_c(1S), eta_c(2S) and non-resonant eta' pi+ pi- production via two-photon collisions

We report the measurement of gamma gamma to eta_c(1S), eta_c(2S) to eta' pi+ pi- with eta' decays to gamma rho and eta pi+ pi- using 941 fb^{-1} of data collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. The eta_c(1S) mass and width are measured to be M = [2984.6\pm0.7 (stat.)\pm2.2 (syst.)] MeV/c^{2} and Γ= [30.8^{+2.3}_{-2.2}~(stat.) \pm 2.5~(syst.)] MeV, respectively. First observation of eta_c(2S) to eta' pi+ pi- with a significance of 5.5sigma including systematic error is obtained, and the eta_c(2S) mass is measured to be M = [3635.1\pm3.7~(stat.)\pm2.9~(syst.)] MeV/c^{2}. The products of the two-photon decay width and branching fraction (B) of decays to eta'pi+ pi- are determined to be Γ_{gamma gamma}B = [65.4\pm2.6~(stat.)\pm6.9~(syst.)] eV for eta_c(1S) and [5.6^{+1.2}_{-1.1}~(stat.)\pm1.1~(syst.)] eV for eta_c(2S). A new decay mode for the eta_c(1S) to eta'f_0(2080) with f_0(2080) to pi+ pi- is observed with a statistical significance of 20sigma. The f_0(2080) mass and width are determined to be M = [2083^{+63}_{-66}~(stat.)\pm 32~(syst.)] MeV/c^{2} and Γ= [178^{+60}_{-178}~(stat.) \pm 55~(syst.)] MeV. The cross sections for gamma gamma to eta' pi+ pi- and eta'f_{2}(1270) are measured for the first time.

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arXiv2018

Measurements of isospin asymmetry and difference of direct $CP$ asymmetries in inclusive $B \to X_s γ$ decays

We report measurements of isospin asymmetry $Δ_{0-}$ and difference of direct $CP$ asymmetries $ΔA_{CP}$ between charged and neutral $B \to X_s γ$ 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 $Δ_{0-} = \bigl[-0.48 \pm 1.49 {\rm (stat.)} \pm 0.97 {\rm (syst.)} \pm 1.15 {(f_{+-}/f_{00})}\bigr]$\% and $ΔA_{CP} = \bigl[+3.69 \pm 2.65 {\rm (stat.)} \pm 0.76{\rm (syst.)}\bigr]$\%, where the last uncertainty for $Δ_{0-}$ is due to the uncertainty on the production ratio of $B^+B^-$ to $B^0\bar{B}^0$ in $Υ(4S)$ decays. The measured value of $Δ_{0-}$ is consistent with zero, allowing us to constrain the resolved photon contribution in the $B \to X_s γ$, and improve the branching fraction prediction. The result for $ΔA_{CP}$ is consistent with the prediction of the SM. We also measure the direct $CP$ asymmetries for charged and neutral $B \to X_s γ$ decays. All the measurements are the most precise to date.

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arXiv2018

Measurement of the branching fraction of $B \rightarrow D^{(*)}π\ellν$ at Belle using hadronic tagging in fully reconstructed events

We report a measurement of the branching fraction of the decay $B \rightarrow D^{(*)}π\ellν$. The analysis uses 772$\times 10^6$ $B\bar{B}$ pairs produced in $e^+e^-\rightarrow Υ(4S)$ data recorded by the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider. The tagging $B$ meson in the decay is fully reconstructed in a hadronic decay mode. On the signal side, we reconstruct the decay $B \rightarrow D^{(*)}π\ellν$ $(\ell=e,μ)$. The measured branching fractions are $\mathcal{B}(B^+ \rightarrow D^-π^+ \ell^+ν)$ = [4.55 $\pm$ 0.27 (stat.) $\pm$ 0.39 (syst.)]$\times 10^{-3}$, $\mathcal{B}(B^0 \rightarrow \bar{D}^0π^- \ell^+ν)$ = [4.05 $\pm$ 0.36 (stat.) $\pm$ 0.41 (syst.)]$\times 10^{-3}$, $\mathcal{B}(B^+ \rightarrow D^{*-}π^+ \ell^+ν)$ = [6.03 $\pm$ 0.43 (stat.) $\pm$ 0.38 (syst.)]$\times 10^{-3}$, and $\mathcal{B}(B^0 \rightarrow \bar{D}^{*0}π^- \ell^+ν)$ = [6.46 $\pm$ 0.53 (stat.) $\pm$ 0.52 (syst.)]$\times 10^{-3}$. These are in good agreement with the current world average values.

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arXiv2018

Production cross sections of hyperons and charmed baryons from $e^+e^-$ annihilation near $\sqrt{s} = 10.52$~GeV

We measure the inclusive production cross sections of hyperons and charmed baryons from $e^+e^-$ annihilation using a 800 fb$^{-1}$ data sample taken near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The feed-down contributions from heavy particles are subtracted using our data, and the direct production cross sections are presented for the first time. The production cross sections divided by the number of spin states for $S=-1$ hyperons follow an exponential function with a single slope parameter except for the $Σ(1385)^+$ resonance. Suppression for $Σ(1385)^+$ and $Ξ(1530)^0$ hyperons is observed. Among the production cross sections of charmed baryons, a factor of three difference for $Λ_c^+$ states over $Σ_c$ states is observed. This observation suggests a diquark structure for these baryons.

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arXiv2018

Inclusive study of bottomonium production in association with an $η$ meson in $e^+e^-$ annihilations near $Υ(5S)$

We study bottomonium production in association with an $η$ meson in $e^+e^-$ annihilations near the $Υ(5S)$, at a center of mass energy of $\sqrt{s}=10.866\,$GeV. The results are based on the $121.4\,$fb$^{-1}$ data sample collected by the Belle experiment at the asymmetric energy KEKB collider. Only the $η$ meson is reconstructed and the missing-mass spectrum of $η$ candidates is investigated. We observe the $e^+e^-\toηΥ_J(1D)$ process and find evidence for the $e^+e^-\toηΥ(2S)$ process, while no significant signals of $Υ(1S)$, $h_b(1P)$, nor $h_b(2P)$ are found. Cross sections for the studied processes are reported.

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arXiv2017

Measurement of branching fraction and direct $CP$ asymmetry in charmless $B^+ \to K^+K^- π^+$ decays at Belle

We report a study of the charmless hadronic decay of the charged $B$ meson to the three-body final state $K^+ K^- π^+$. The results are based on a data sample that contains $772\times10^6$ $B \bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The measured inclusive branching fraction and the direct $CP$ asymmetry are $(5.38\pm0.40\pm0.35)\times 10^{-6}$ and $-0.170\pm0.073\pm0.017$, respectively, where the first uncertainties are statistical and the second are systematic. The $K^{+}K^{-}$ invariant mass distribution of the signal candidates shows an excess in the region below $1.5$ GeV/$c^2$, which is consistent with the previous studies from BaBar and LHCb. In addition, strong evidence of a large direct $CP$ asymmetry is found in the $K^{+}K^{-}$ low-invariant-mass region.

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arXiv2017

Measurement of the Decays $\boldsymbol{B\toη\ellν_\ell}$ and $\boldsymbol{B\toη^\prime\ellν_\ell}$ in Fully Reconstructed Events at Belle

We report branching fraction measurements of the decays $B^+\toη\ell^+ν_\ell$ and $B^+\toη^\prime\ell^+ν_\ell$ based on 711~fb$^{-1}$ of data collected near the $Υ(4S)$ resonance with the Belle experiment at the KEKB asymmetric-energy $e^+e^-$ collider. This data sample contains 772 million $B\bar B$~events. One of the two $B$~mesons is fully reconstructed in a hadronic decay mode. Among the remaining ("signal-$B$") daughters, we search for the $η$~meson in two decay channels, $η\toγγ$ and $η\toπ^+π^-π^0$, and reconstruct the $η^{\prime}$~meson in $η^\prime\toηπ^+π^-$ with subsequent decay of the $η$ into $γγ$. Combining the two $η$ modes and using an extended maximum likelihood, the $B^+\toη\ell^+ν_\ell$ branching fraction is measured to be $(4.2\pm 1.1 (\rm stat.)\pm 0.3 (\rm syst.))\times 10^{-5}$. For $B^+\toη^\prime\ell^+ν_\ell$, we observe no significant signal and set an upper limit of $0.72\times 10^{-4}$ at 90\% confidence level.

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