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Belle Collaboration

Publications and source records attributed to Belle Collaboration.

At least 127 records · Page 7Linked to original sources

arXiv2019

Search for $Ω(2012)\to KΞ(1530) \to KπΞ$ at Belle

Using data samples of $e^+e^-$ collisions collected at the $Υ(1S)$, $Υ(2S)$, and $Υ(3S)$ resonances with the Belle detector, we search for the three-body decay of the $Ω(2012)$ baryon to $KπΞ$. This decay is predicted to dominate for models describing the $Ω(2012)$ as a $KΞ(1530)$ molecule. No significant $Ω(2012)$ signals are observed in the studied channels, and 90\% credibility level upper limits on the ratios of the branching fractions relative to $K Ξ$ decay modes are obtained.

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arXiv2019

Measurement of branching fraction and final-state asymmetry for the $\bar{B}^{0}\to K^{0}_{S}K^{\mp}π^{\pm}$ decay

We report a measurement of the branching fraction and final-state asymmetry for the $\bar{B}^{0}\to K^{0}_{S}K^{\mp}π^{\pm}$ decays. The analysis is based on a data sample of 711 $\rm{fb}^{-1}$ collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. We obtain a branching fraction of $(3.60\pm0.33\pm0.15)\times10^{-6}$ and a final-state asymmetry of $(-8.5\pm8.9\pm0.2)\%$, where the first uncertainties are statistical and the second are systematic. Hints of peaking structures are seen in the differential branching fractions measured as functions of Dalitz variables.

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arXiv2019

Evidence for the decay $B^0\to p\bar{p}π^0$

We report a search for the charmless baryonic decay $B^0\to p\bar{p}π^0$ with a data sample corresponding to an integrated luminosity of 711~$\rm fb^{-1}$ containing $(772\pm 10)\times 10^6$ $B^0\bar{B}^0$ pairs. The data was collected by the Belle experiment running on the $Υ(4S)$ resonance at the KEKB $e^+e^-$ collider. We measure a branching fraction $\mathcal{B}(B^0\to p\bar{p}π^0)= (5.0\pm1.8\pm0.6 )\times 10^{-7}$, where the first uncertainty is statistical and the second is systematic. The signal has a significance of 3.1 standard deviations and constitutes the first evidence for this decay mode. We also search for the intermediate two-body decays $B^{0}\toΔ^+\bar{p}$ and $B^0\to\barΔ^-p$, and set an upper limit on the branching fraction: $\mathcal{B}(B^0\to Δ^+\bar{p})+\mathcal{B}(B^0\to\barΔ^-p)<1.6\times10^{-6}$ at 90% confidence level.

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arXiv2019

Measurement of the $D^{\ast-}$ polarization in the decay $B^0 \to D^{\ast -}τ^+ν_τ$

We report the first measurement of the $D^{\ast -}$ meson polarization in the decay $B^0 \to D^{*-} τ^+ν_τ$ using the full data sample of 772$\times 10^6$ $B\bar{B}$ pairs recorded with the Belle detector at the KEKB electron-positron collider. Our result, $F_L^{D^\ast} = 0.60 \pm 0.08 ({\rm stat}) \pm 0.04 ({\rm sys})$, where $F_L^{D^\ast}$ denotes the $D^{\ast-}$ meson longitudinal polarization fraction, agrees within about $1.7$ standard deviations of the standard model prediction.

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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

Search for $CP$ violation with kinematic asymmetries in the $D^0 \to K^+ K^- π^+ π^-$ decay

We search for $CP$ violation in the singly-Cabibbo-suppressed decay $D^{0}\rightarrow K^{+}K^{-}π^{+}π^{-}$ using data corresponding to an integrated luminosity of $988\text{ }{\rm fb}^{-1}$ collected by the Belle detector at the KEKB $e^{+}e^{-}$ collider. We measure a set of five kinematically dependent $CP$ asymmetries, of which four asymmetries are measured for the first time. The set of asymmetry measurements can be sensitive to $CP$ violation via interference between the different partial-wave contributions to the decay and performed on other pseudoscalar decays. We find no evidence of $CP$ violation.

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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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arXiv2019

Search for a light CP-odd Higgs boson and low-mass dark matter at the Belle experiment

We report on the first Belle search for a light CP-odd Higgs boson, $A^{0}$, that decays into low mass dark matter, $χ$, in final states with a single photon and missing energy. We search for events produced via the dipion transition $Υ(\textrm{2S})\rightarrowΥ(\textrm{1S})π^{+}π^{-}$, followed by the on-shell process $Υ(\textrm{1S})\rightarrowγA^{0}$ with $A^{0} \rightarrowχχ$, or by the off-shell process $Υ(\textrm{1S})\rightarrowγχχ$. Utilizing a data sample of 157.3 $\times$ 10$^{6}$ $Υ(\textrm{2S})$ decays, we find no evidence for a signal. We set limits on the branching fractions of such processes in the mass ranges $M_{A^{0}} <$ 8.97 $\textrm{GeV/}\textit{c}^{2}$ and $M_χ <$ 4.44 $\textrm{GeV/}\textit{c}^{2}$. We then use the limits on the off-shell process to set competitive limits on WIMP-nucleon scattering in the WIMP mass range below 5 $\textrm{GeV/}\textit{c}^{2}$.

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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

Observation of $Υ(2S)\toγη_{b}(1S)$ decay

We report the observation of $Υ(2S)\toγη_{b}(1S)$ decay based on analysis of the inclusive photon spectrum of $24.7$ fb$^{-1}$ of $e^+ e^-$ collisions at the $Υ(2S)$ center-of-mass energy collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We measure a branching fraction of $\mathcal{B}(Υ(2S)\toγη_{b}(1S))=(6.1^{+0.6+0.9}_{-0.7-0.6})\times 10^{-4}$, and derive an $η_{b}(1S)$ mass of $9394.8^{+2.7+4.5}_{-3.1-2.7}$ MeV/$c^{2}$, where the uncertainties are statistical and systematic, respectively. The significance of our measurement is greater than 7 standard deviations, constituting the first observation of this decay mode.

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arXiv2018

Observation of $e^+e^- \to γχ_{c1}$ and search for $e^+e^- \to γχ_{c0}, γχ_{c2},$ and $γη_c$ at $\sqrt{s}$ near 10.6 GeV at Belle

Using data samples of 89.5~fb$^{-1}$, 711.0~fb$^{-1}$, and 121.4~fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider at center-of-mass energies 10.52 GeV, 10.58 GeV, and 10.867 GeV, respectively, we study the exclusive reactions $e^+e^-\toγχ_{cJ}$ ($J = 0,~1,~2$) and $e^+e^-\toγη_c$. A significant $γχ_{c1}$ signal is observed for the first time at $\sqrt{s}=10.58$ GeV with a significance of $5.1σ$ including systematic uncertainties. No significant excesses for $γχ_{c0}$, $γχ_{c2}$, and $γη_c$ final states are found, and we set 90\% credibility level upper limits on the Born cross sections ($σ_{\rm B}$) at 10.52 GeV, 10.58 GeV, and 10.867~GeV. Together with cross sections measured by BESIII at lower center-of-mass energies, the energy dependency of $σ_{\rm B}(e^+e^-\toγχ_{c1})$ is obtained.

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arXiv2018

Measurement of the Decays $Λ_c\to Σππ$ at Belle

We report measurements of the branching fractions of the decays $Λ^+_c\toΣ^+π^-π^+$, $Λ^+_c\toΣ^0π^+π^0$ and $Λ^+_c\toΣ^+π^0π^0$ relative to the reference channel $Λ^+_c\to pK^-π^+$. The analysis is based on the full data sample collected at and close to $Υ(4S)$ resonance by the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider corresponding to the integrated luminosity of 711 fb$^{-1}$. We measure ${\cal B}(Λ^+_c\rightarrowΣ^+π^-π^+)/{\cal B}(Λ^+_c\to pK^-π^+) = 0.706~\pm 0.003~\pm 0.029$, ${\cal B}(Λ^+_c\rightarrowΣ^0π^+π^0)/{\cal B}(Λ^+_c\to pK^-π^+) = 0.491~\pm 0.005~\pm 0.028$ and ${\cal B}(Λ^+_c\rightarrowΣ^+π^0π^0)/{\cal B}(Λ^+_c\to pK^-π^+) = 0.198~\pm 0.006~\pm 0.016$. The listed uncertainties are statistical and systematic, respectively.

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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

Search for the lepton-flavor-violating decay $B^{0}\to K^{\ast 0} μ^{\pm} e^{\mp}$

We have searched for the lepton-flavor-violating decay $B^{0}\to K^{\ast 0} μ^{\pm} e^{\mp}$ using a data sample of 711 $fb^{-1}$ that contains $772 \times 10^{6}$ $B\bar{B}$ pairs. The data were collected near the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. No signals were observed, and we set 90% confidence level upper limits on the branching fractions of ${\cal B}(B^{0}\to K^{\ast 0} μ^{+} e^{-})< 1.2\times 10^{-7}$, ${\cal B}(B^{0}\to K^{\ast 0} μ^{-} e^{+})< 1.6\times 10^{-7}$, and, for both decays combined, ${\cal B}(B^{0}\to K^{\ast 0} μ^{\pm} e^{\mp}) < 1.8\times 10^{-7}$. These are the most stringent limits on these decays to date.

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arXiv2018

Observation of $Ξ_{c}(2930)^0$ and updated measurement of $B^{-} \to K^{-} Λ_{c}^{+} \barΛ_{c}^{-}$ at Belle

We report the first observation of the $Ξ_{c}(2930)^0$ charmed-strange baryon with a significance greater than 5$σ$. The $Ξ_{c}(2930)^0$ is found in its decay to $K^- Λ_{c}^+$ in $B^{-} \to K^{-} Λ_{c}^{+} \barΛ_{c}^{-}$ decays. The measured mass and width are $[2928.9 \pm 3.0(\rm stat.)^{+0.9}_{-12.0}(\rm syst.)]$ MeV/$c^{2}$ and $[19.5 \pm 8.4(\rm stat.) ^{+5.9}_{-7.9}(\rm syst.)]$ MeV, respectively, and the product branching fraction is ${\cal B}(B^{-} \to Ξ_{c}(2930)^0 \barΛ_{c}^{-}) {\cal B}(Ξ_{c}(2930)^0 \to K^- Λ_{c}^{+})=[1.73 \pm 0.45(\rm stat.) \pm 0.21(\rm syst.)]\times 10^{-4}$. We also measure ${\cal B}(B^{-} \to K^{-} Λ_{c}^{+} \barΛ_{c}^{-}) = [4.80 \pm 0.43(\rm stat.) \pm 0.60(\rm syst.)] \times 10^{-4}$ with improved precision, and 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 $Y(4660)$ nor its spin partner 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

Observation of Transverse $Λ/\barΛ$ Hyperon Polarization in $e^+e^-$ Annihilation at Belle

We report the first observation of the spontaneous polarization of $Λ$ and $\barΛ$ hyperons transverse to the production plane in $e^+e^-$ annihilation, which is attributed to the effect arising from a polarizing fragmentation function. For inclusive $Λ/\barΛ$ production, we also report results with subtracted feed-down contributions from $Σ^0$ and charm. This measurement uses a dataset of 800.4 fb$^{-1}$ collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV. We observe a significant polarization that rises with the fractional energy carried by the $Λ/\barΛ$ hyperon.

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arXiv2018

Search for $Υ(1S,2S) \to Z^{+}_{c}Z^{(\prime) -}_{c}$ and $e^{+}e^{-} \to Z^{+}_{c}Z^{(\prime) -}_{c}$ at $\sqrt{s}$ = 10.52, 10.58, and 10.867 GeV

The first search for $Z_{c}$ pair production in $Υ(1S)$ and $Υ(2S)$ decays and in $e^{+}e^{-}$ annihilation at $\sqrt{s}$ = 10.52, 10.58, and 10.867 GeV is conducted using data collected with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant signals are observed in any of the studied modes, and the 90\% credibility level upper limits on their product branching fractions in $Υ(1S)$ and $Υ(2S)$ decays (${\cal B}(Υ(1S,2S)\to Z^{+}_{c}Z^{(\prime) -}_{c})\times{\cal B}(Z^{+}_{c}\toπ^{+}+c\bar c)$ ($c\bar c=J/ψ$, $χ_{c1}(1P)$, $ψ(2S)$)) and the product of Born cross section and branching fraction for $e^{+}e^{-} \to Z^{+}_{c}Z^{(\prime) -}_{c}$ ($σ(e^+e^- \to Z^{+}_{c}Z^{(\prime) -}_{c})\times {\cal B}(Z^{+}_{c} \to π^+ +c\bar c)$) at $\sqrt{s}$ = 10.52, 10.58, and 10.867 GeV are determined. Here, $Z_{c}$ refers to the $Z_{c}(3900)$ and $Z_{c}(4200)$ observed in the $πJ/ψ$ final state, the $Z_{c1}(4050)$ and $Z_{c2}(4250)$ in the $πχ_{c1}(1P)$ state, and the $Z_{c}(4050)$ and $Z_{c}(4430)$ in the $πψ(2S)$ state.

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arXiv2018

Observation of $Υ(4S)\to η' Υ(1S)$

We report the first observation of the hadronic transition $Υ(4S)\toη'Υ(1S)$, using 496 fb$^{-1}$ data collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. We reconstruct the $η'$ meson through its decays to $ρ^0γ$ and to $π^+π^-η$, with $η\toγγ$. We measure: ${\cal B}(Υ(4S)\toη'Υ(1S))=(3.43\pm 0.88 {\rm(stat.)} \pm 0.21 {\rm(syst.)})\times10^{-5}$, with a significance of 5.7$σ$.

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