arXiv subjects

K. -H. Kim

Publications and source records attributed to K. -H. Kim.

At least 73 records · Page 4Linked to original sources

arXiv2022

Search for a light Higgs boson in single-photon decays of $Υ(1S)$ using $Υ(2S) \to π^+ π^- Υ(1S)$ tagging method

We search for a light Higgs boson ($A^0$) decaying into a $τ^+τ^-$ or $μ^+μ^-$ pair in the radiative decays of $Υ(1S)$. The production of $Υ(1S)$ mesons is tagged by $Υ(2S)\to π^+ π^- Υ(1S)$ transitions, using 158 million $Υ(2S)$ events accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant $A^0$ signals in the mass range from the $τ^+τ^-$ or $μ^+μ^-$ threshold to 9.2 GeV/$c^2$ are observed. We set the upper limits at 90\% credibility level (C.L.) on the product branching fractions for $Υ(1S)\to γA^0$ and $A^0\to τ^+τ^-$ varying from $3.8\times10^{-6}$ to $1.5\times10^{-4}$. Our results represent an approximately twofold improvement on the current world best upper limits for the $Υ(1S)\to γA^0(\to τ^+τ^-)$ production. For $A^0\to μ^+μ^-$, the upper limits on the product branching fractions for $Υ(1S)\to γA^0$ and $A^0\to μ^+μ^-$ are at the same level as the world average limits, and vary from $3.1\times10^{-7}$ to $1.6\times10^{-5}$. The upper limits at 90\% C.L. on the Yukawa coupling $f_{Υ(1S)}$ and mixing angle ${\rm sin}θ_{A^0}$ are also given.

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arXiv2022

Search for tetraquark states $X_{cc\bar{s}\bar{s}}$ in $D_{s}^{+}D_{s}^{+}~(D_{s}^{+}D_{s}^{+})$ final states at Belle

A search for double-heavy tetraquark state candidates $X_{cc\bar{s}\bar{s}}$ decaying to $D_{s}^{+}D_{s}^{+}$ and $D_{s}^{*+} D_{s}^{*+}$ is presented for the first time using the data samples of 102 million $Υ(1S)$ and 158 million $Υ(2S)$ events, and the data samples at $\sqrt{s}$ = 10.52~GeV, 10.58~GeV, and 10.867~GeV corresponding to integrated luminosities of 89.5~fb$^{-1}$, 711.0~fb$^{-1}$, and 121.4~fb$^{-1}$, respectively, accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. The invariant-mass spectra of the $D_{s}^{+}D_{s}^{+}$ and $D_{s}^{*+} D_{s}^{*+}$ are studied to search for possible resonances. No significant signals are observed, and the 90\% confidence level upper limits on the product branching fractions [${\cal B}(Υ(1S,2S) \to X_{cc\bar{s}\bar{s}} + anything) \times {\cal B}(X_{cc\bar{s}\bar{s}} \to D_{s}^{+}D_{s}^{+}(D_{s}^{*+} D_{s}^{*+}))$] in $Υ(1S,2S)$ inclusive decays and the product values of Born cross section and branching fraction [$σ(e^+e^- \to X_{cc\bar{s}\bar{s}} + anything ) \times {\cal B}(X_{cc\bar{s}\bar{s}} \to D_{s}^{+}D_{s}^{+}(D_{s}^{*+} D_{s}^{*+}))$] in $e^+e^-$ collisions at $\sqrt{s}$ = 10.52~GeV, 10.58~GeV, and 10.867~GeV under different assumptions of $X_{cc\bar{s}\bar{s}}$ masses and widths are obtained.

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arXiv2022

Study of $\overline{B}{}^0\rightarrow D^{+}h^{-} (h=K/π)$ decays at Belle

We present a measurement of the branching fractions of the Cabibbo favored $\overline{B}{}^0\rightarrow D^{+}π^{-}$ and the Cabibbo suppressed $\overline{B}{}^0\rightarrow D^{+}K^{-}$ decays. We find $\mathcal{B}(\overline{B}{}^0\rightarrow D^{+}π^{-}) = (2.48 \pm 0.01 \pm 0.09 \pm 0.04) \times 10^{-3}$ and $\mathcal{B}(\overline{B}{}^0\rightarrow D^{+}K^{-})= (2.03 \pm 0.05 \pm 0.07 \pm 0.03) \times 10^{-4}$ decays, where the first uncertainty is statistical, the second is systematic, and the third uncertainty is due to the $D^{+} \rightarrow K^{-}π^{+}π^{+}$ branching fraction. The ratio of branching fractions of $\overline{B}{}^0\rightarrow D^{+}K^{-}$ and $\overline{B}{}^0\rightarrow D^{+}π^{-}$ is measured to be $R^{D} = [8.19 \pm 0.20(\rm stat) \pm 0.23(\rm syst)] \times 10^{-2} $. These measurements are performed using the full Belle data set, which corresponds to $772 \times 10^{6} B\overline{B} $ pairs.

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arXiv2022

Search for the decay $B_s^0 \to η^\prime K_S^0$

We report the results of the first search for the decay $B_s^0 \to η^\prime K_S^0$ using $121.4\,{\rm fb}^{-1}$ of data collected at the $Υ(5S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We observe no signal and set a 90\% confidence-level upper limit of $8.16 \times 10^{-6}$ on the $B_s^0 \to η^\prime K_S^0$ branching fraction.

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arXiv2022

Measurement of Two-Particle Correlations of Hadrons in $e^{+}e^{-}$ Collisions at Belle

The measurement of two-particle angular correlation functions in high-multiplicity $e^+e^-$ collisions at $\sqrt{s}=10.52$ GeV is reported. In this study, the $89.5~{\text{fb}}^{-1}$ of hadronic $e^+e^-$ annihilation data collected by the Belle detector at KEKB are used. Two-particle angular correlation functions are measured in the full relative azimuthal angle ($Δϕ$) and three units of pseudorapidity ($Δη$), defined by either the electron beam axis or the event-shape thrust axis, and are studied as a function of charged-particle multiplicity. The measurement in the thrust axis analysis, with mostly outgoing quark pairs determining the reference axis, is sensitive to the region of additional soft gluon emissions. No significant anisotropic collective behavior is observed with either coordinate analyses. Near-side jet correlations appear to be absent in the thrust axis analysis. The measurements are compared to predictions from various event generators and are expected to provide new constraints to the phenomenological models in the low-energy regime.

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arXiv2021

Measurements of $q^2$ Moments of Inclusive $B \rightarrow X_c \ell^+ ν_{\ell}$ Decays with Hadronic Tagging

We present the measurement of the first to fourth order moments of the four-momentum transfer squared, $q^2$, of inclusive $B \rightarrow X_c \ell^+ ν_{\ell}$ decays using the full Belle data set of 711 $\mathrm{fb}^{-1}$ of integrated luminosity at the $Υ(4S)$ resonance where $\ell = e, μ$. The determination of these moments and their systematic uncertainties open new pathways to determine the absolute value of the CKM matrix element $V_{cb}$ using a reduced set of matrix elements of the heavy quark expansion. In order to identify and reconstruct the $X_c$ system, we reconstruct one of the two $B$-mesons using machine learning techniques in fully hadronic decay modes. The moments are measured with progressively increasing threshold selections on $q^2$ starting with a lower value of 3.0 $\mathrm{GeV}^2$ in steps of 0.5 $\mathrm{GeV}^2$ up to a value of 10.0 $\mathrm{GeV}^2$. The measured moments are further unfolded, correcting for reconstruction and selection effects as well as QED final state radiation. We report the moments separately for electron and muon final states and observe no lepton flavor universality violating effects.

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arXiv2021

Search for $B^{0} \to τ^\pm \ell^\mp$ ($\ell=e,μ$) with a hadronic tagging method at Belle

We present a search for the lepton-flavor-violating decays $B^{0} \to τ^\pm \ell^\mp$, where $\ell=(e,\,μ)$, using the full data sample of $772 \times 10^6$ $B \overline{B}$ pairs recorded by the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We use events in which one $B$ meson is fully reconstructed in a hadronic decay mode. The $τ^\pm$ lepton is reconstructed indirectly using the momentum of the reconstructed $B$ and that of the $\ell^\mp$ from the signal decay. We find no evidence for $B^{0} \to τ^\pm \ell^\mp$ decays and set upper limits on their branching fractions at 90% confidence level of $\cal B$($B^{0} \to τ^\pm μ^{\mp}$)$ < 1.5 \times 10^{-5}$ and $\cal B$($B^{0} \to τ^\pm e^{\mp}$)$ < 1.6 \times 10^{-5}$.

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arXiv2021

Measurement of the branching fraction of $Λ_c^+ \to p ω$ decay at Belle

Using 980.6 $\rm fb^{-1}$ of data collected with the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider, we present a measurement of the branching fraction of the singly Cabibbo-suppressed decay $Λ_c^+ \to p ω$. A clear $Λ_c^+$ signal is observed for $Λ_c^+ \to p ω$ with a statistical significance of 9.1 standard deviations, and we measure the ratio of branching fractions ${\cal B}(Λ_c^+ \to p ω)/{\cal B}(Λ_c^+ \to p K^- π^+) = (1.32 \pm 0.12 (\rm stat) \pm 0.10 (\rm syst))\times 10^{-2}$, from which we infer the branching fraction ${\cal B}(Λ_c^+ \to p ω) = (8.27 \pm 0.75 (\rm stat) \pm 0.62 (\rm syst) \pm 0.42 (\rm ref))\times 10^{-4}$. The first quoted uncertainty is statistical, the second systematic, and the third from the reference mode $Λ_c^+ \to p K^- π^+$.

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arXiv2021

Measurement of branching fractions and search for $CP$ violation in $D^{0}\toπ^{+}π^{-}η$, $D^{0}\to K^{+}K^{-}η$, and $D^{0}\toϕη$ at Belle

We measure the branching fractions and $CP$ asymmetries for the singly Cabibbo-suppressed decays $D^{0}\toπ^{+}π^{-}η$, $D^{0}\to K^{+}K^{-}η$, and $D^{0}\toϕη$, using 980 fb$^{-1}$ of data from the Belle experiment at the KEKB $e^+e^-$ collider. We obtain \begin{eqnarray} \mathcal{B}(D^{0}\toπ^{+}π^{-}η) & = & [1.22\pm 0.02\,({\rm stat})\pm 0.02\,({\rm syst})\pm 0.03\,(\mathcal{B}_{\rm ref})]\times 10^{-3}\,, \nonumber \\ \mathcal{B}(D^{0}\to K^{+}K^{-}η) & = & [1.80\,^{+0.07}_{-0.06}\,({\rm stat})\pm 0.04\,({\rm syst})\pm 0.05\,(\mathcal{B}_{\rm ref})]\times 10^{-4}\,, \nonumber \\ \mathcal{B}(D^{0}\toϕη) & = & [1.84\pm 0.09\,({\rm stat})\pm 0.06\,({\rm syst})\pm 0.05\,(\mathcal{B}_{\rm ref})]\times 10^{-4}\,, \nonumber \end{eqnarray} where the third uncertainty ($\mathcal{B}_{\rm ref}$) is from the uncertainty in the branching fraction of the reference mode $D^{0}\to K^{-}π^{+}η$. The color-suppressed decay $D^{0}\toϕη$ is observed for the first time, with very high significance. The results for the $CP$ asymmetries are \begin{eqnarray} A_{CP}(D^{0}\toπ^{+}π^{-}η) & = & [0.9\pm 1.2\,({\rm stat})\pm 0.5\,({\rm syst})]\%\,, \nonumber \\ A_{CP}(D^{0}\to K^{+}K^{-}η) & = & [-1.4\pm 3.3\,({\rm stat})\pm 1.1\,({\rm syst})]\%\,, \nonumber \\ A_{CP}(D^{0}\toϕη)&= & [-1.9\pm 4.4\,({\rm stat})\pm 0.6\,({\rm syst})]\%\,. \nonumber \end{eqnarray} The results for $D^{0}\toπ^{+}π^{-}η$ are a significant improvement over previous results. The branching fraction and $A_{CP}$ results for $D^{0}\to K^{+}K^{-}η$, and the $A_{CP}$ result for $D^{0}\toϕη$, are the first such measurements. No evidence for $CP$ violation is found in any of these decays.

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arXiv2021

Measurement of the Masses and Widths of the $Σ_c(2455)^+$ and $Σ_c(2520)^+$ Baryons

Using 980 ${\rm fb}^{-1}$ of data {collected} with the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider, we report the measurements of the masses, and the first measurements of the instrinsic widths, of the $Σ_c(2455)^+$ and $Σ_c(2520)^+$ charmed baryons. We find $M(Σ_c(2455)^+)-M(Λ_c^+) = 166.17\pm 0.05^{+0.16}_{-0.07}\ {\rm MeV}/c^2$, $Γ(Σ_c(2455)^+) = 2.3 \pm 0.3 \pm 0.3\ {\rm MeV/c^2}$, $M(Σ_c(2520)^+)-M(Λ_c^+) = 230.9 \pm 0.5 ^{+0.5}_{-0.1}\ {\rm MeV}/c^2$, and $Γ(Σ_c(2520)^+) = 17.2^{+2.3\ +3.1}_{-2.1\ -0.7}\ {\rm MeV}/c^2$, where the uncertainties are statistical and systematic, respectively. These measurements can be used to test models of the underlying quark structure of the $Σ_c$ states.

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arXiv2021

Search for lepton-flavor-violating tau-lepton decays to $\ellγ$ at Belle

Charged lepton flavor violation is forbidden in the Standard Model but possible in several new physics scenarios. In many of these models, the radiative decays $τ^{\pm}\rightarrow\ell^{\pm}γ$ ($\ell=e,μ$) are predicted to have a sizeable probability, making them particularly interesting channels to search at various experiments. An updated search via $τ^{\pm}\rightarrow\ell^{\pm}γ$ using full data of the Belle experiment, corresponding to an integrated luminosity of 988 fb$^{-1}$, is reported for charged lepton flavor violation. No significant excess over background predictions from the Standard Model is observed, and the upper limits on the branching fractions, $\mathcal{B}(τ^{\pm}\rightarrow μ^{\pm}γ)$ $\leq$ $4.2\times10^{-8}$ and $\mathcal{B}(τ^{\pm}\rightarrow e^{\pm}γ)$ $\leq$ $5.6\times10^{-8}$, are set at 90\% confidence level.

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arXiv2021

Measurements of the branching fractions of the semileptonic decays $Ξ_{c}^{0} \to Ξ^{-} \ell^{+} ν_{\ell}$ and the asymmetry parameter of $Ξ_{c}^{0} \to Ξ^{-} π^{+}$

Using data samples of 89.5 and 711 fb$^{-1}$ recorded at energies of $\sqrt{s}=10.52$ and $10.58$ GeV, respectively, with the Belle detector at the KEKB $e^+e^-$ collider, we report measurements of branching fractions of semileptonic decays $Ξ_{c}^{0} \to Ξ^{-} \ell^{+} ν_{\ell}$ ($\ell=e$ or $μ$) and the $CP$-asymmetry parameter of $Ξ_{c}^{0} \to Ξ^{-} π^{+}$ decay. The branching fractions are measured to be ${\cal B}(Ξ_{c}^{0} \to Ξ^{-} e^{+} ν_{e})=(1.31 \pm 0.04 \pm 0.07 \pm 0.38)\%$ and ${\cal B}(Ξ_{c}^{0} \to Ξ^{-} μ^{+} ν_μ)=(1.27 \pm 0.06 \pm 0.10 \pm 0.37)\%$, and the decay parameter $α_{Ξπ}$ is measured to be $0.63 \pm 0.03 \pm 0.01$ with much improved precision compared to the current world average. The corresponding ratio ${\cal B}(Ξ_{c}^{0} \to Ξ^{-} e^{+} ν_{e})/{\cal B}(Ξ_{c}^{0} \to Ξ^{-} μ^{+} ν_μ)$ is $1.03 \pm 0.05\pm 0.07$, which is consistent with the expectation of lepton flavor universality. The first measured asymmetry parameter ${\cal A}_{CP} = (α_{Ξ^{-}π^{+}} + α_{\barΞ^{+}π^{-}})/(α_{Ξ^{-}π^{+}} - α_{\barΞ^{+}π^{-}}) = 0.024 \pm 0.052 \pm 0.014$ is found to be consistent with zero. The first and the second uncertainties above are statistical and systematic, respectively, while the third ones arise due to the uncertainty of the $Ξ_{c}^{0} \to Ξ^{-} π^+$ branching fraction.

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arXiv2021

Study of $e^+e^-\to Υ(\rm1S,2S)η$ and $e^+e^-\to Υ(\rm 1S)η^{\prime}$ at $\sqrt{s}=10.866$ GeV with the Belle detector

We report the first observation of the processes $e^+e^-\toΥ(\rm 1S,2S)η$ at $\sqrt{s}=10.866$~GeV with a $10.2σ$ and $16.5σ$ significance respectively. The measured Born cross sections are $σ(e^+e^- \to Υ(2S)η)=2.07 \pm 0.21 \pm 0.19$~pb, and $σ(e^+e^- \to Υ(\rm 1S)η)=0.42 \pm 0.08 \pm 0.04$~pb. We also set the upper limit on the cross section of the process $e^+e^- \to Υ(\rm 1S)η^{\prime}$ to be $σ(e^+e^- \to Υ(\rm 1S)η^{\prime})<0.035$~pb at $90\%$ CL. The results are obtained with the data sample collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider in the energy range from $10.63$~GeV to $11.02$~GeV.

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arXiv2021

Measurements of branching fractions and asymmetry parameters of $Ξ^0_c\to Λ\bar K^{0}$, $Ξ^0_c\to Σ^0\bar K^{0}$, and $Ξ^0_c\to Σ^+K^{*-}$ decays at Belle

Using a data sample of 980 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider, we study the processes of $Ξ^0_c\to Λ\bar K^{*0}$, $Ξ^0_c\to Σ^0\bar K^{*0}$, and $Ξ^0_c\to Σ^+K^{*-}$ for the first time. The relative branching ratios to the normalization mode of $Ξ^0_c\toΞ^-π^+$ are measured to be $${\cal B}(Ξ^0_c\to Λ\bar K^{*0})/{\cal B}(\xic\to Ξ^-π^+)=0.18\pm0.02({\rm stat.})\pm0.01({\rm syst.}),$$ $${\cal B}(Ξ^0_c\to Σ^0\bar K^{*0})/{\cal B}(\xic\to Ξ^-π^+)=0.69\pm0.03({\rm stat.})\pm0.03({\rm syst.}),$$ $${\cal B}(Ξ^0_c\to Σ^+K^{*-})/{\cal B}(\xic\to Ξ^-π^+)=0.34\pm0.06({\rm stat.})\pm0.02({\rm syst.}),$$ where the uncertainties are statistical and systematic, respectively. We obtain %measure the branching fractions of $Ξ^0_c\to Λ\bar K^{*0}$, $Ξ^0_c\to Σ^0\bar K^{*0}$, and $Ξ^0_c\to Σ^+K^{*-}$ to be $${\cal B}(Ξ^0_c\to Λ\bar K^{*0})=(3.3\pm0.3({\rm stat.})\pm0.2({\rm syst.})\pm1.0({\rm ref.}))\times10^{-3},$$ $${\cal B}(Ξ^0_c\to Σ^0\bar K^{*0})=(12.4\pm0.5({\rm stat.})\pm0.5({\rm syst.})\pm3.6({\rm ref.}))\times10^{-3},$$ $${\cal B}(Ξ^0_c\to Σ^+K^{*-})=(6.1\pm1.0({\rm stat.})\pm0.4({\rm syst.})\pm1.8({\rm ref.}))\times10^{-3},$$ where the uncertainties are statistical, systematic, and from ${\cal B}(\xic \to Ξ^-π^+)$, respectively. The asymmetry parameters $α(Ξ^0_c\to Λ\bar K^{*0})$ and $α(Ξ^0_c\to Σ^+K^{*-})$ are $0.15\pm0.22({\rm stat.})\pm0.04({\rm syst.})$ and $-0.52\pm0.30({\rm stat.})\pm0.02({\rm syst.})$, respectively, where the uncertainties are statistical followed by systematic.

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arXiv2021

Search for the $η_{c2}(1D)$ in $e^+e^-\toγη_{c2}(1D)$ at $\sqrt{s}$ near 10.6 GeV at Belle

For the first time we search for the $η_{c2}(1D)$ in $e^+e^-\toγη_{c2}(1D)$ at $\sqrt{s}$ = 10.52, 10.58, and 10.867 GeV with data samples of 89.5 fb$^{-1}$, 711 fb$^{-1}$, and 121.4 fb$^{-1}$, respectively, accumulated with the Belle detector at the KEKB asymmetric energy electron-positron collider. No significant $η_{c2}(1D)$ signal is observed in the mass range between 3.8 and 3.88 GeV/$c^2$. The upper limit at 90\% confidence level on the product of the Born cross section for $e^+e^- \to γη_{c2}(1D)$ and branching fraction for $η_{c2}(1D)\to γh_c(1P)$ is determined to be $σ(e^+e^- \to γη_{c2}(1D)){\cal B}(η_{c2}(1D)\to γh_c(1P))$ $<$ 4.9 fb at $\sqrt{s}$ near 10.6 GeV.

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arXiv2021

Measurements of Partial Branching Fractions of Inclusive $B \to X_u \, \ell^+\, ν_{\ell}$ Decays with Hadronic Tagging

We present measurements of partial branching fractions of inclusive semileptonic $B \to X_u \, \ell^+\, ν_{\ell}$ decays using the full Belle data set of 711 fb$^{-1}$ of integrated luminosity at the $Υ(4S)$ resonance and for $\ell = e, μ$. Inclusive semileptonic $B \to X_u \, \ell^+\, ν_{\ell}$ decays are CKM suppressed and measurements are complicated by the large background from CKM-favored $B \to X_c \, \ell^+\, ν_{\ell}$ transitions, which have a similar signature. Using machine learning techniques, we reduce this and other backgrounds effectively, whilst retaining access to a large fraction of the $B \to X_u \, \ell^+\, ν_{\ell}$ phase space and high signal efficiency. We measure partial branching fractions in three phase-space regions covering about $31\%$ to $86\%$ of the accessible $B \to X_u \, \ell^+\, ν_{\ell}$ phase space. The most inclusive measurement corresponds to the phase space with lepton energies of $E_\ell^B > 1 $ GeV, and we obtain $Δ\mathcal{B}(B \to X_u \ell^+ \, ν_\ell) = \left( 1.59 \pm 0.07 \pm 0.16 \right) \times 10^{-3}$ from a two-dimensional fit of the hadronic mass spectrum and the four-momentum-transfer squared distribution, with the uncertainties denoting the statistical and systematic error. We find $\left| V_{ub} \right| = \left( 4.10 \pm 0.09 \pm 0.22 \pm 0.15 \right) \times 10^{-3}$ from an average of four calculations for the partial decay rate with the third uncertainty denoting the average theory error. This value is higher but compatible with the determination from exclusive semileptonic decays within 1.3 standard deviations. In addition, we report charmless inclusive partial branching fractions separately for $B^+$ and $B^0$ mesons as well as for electron and muon final states. No isospin breaking or lepton flavor universality violating effects are observed.

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arXiv2021

Evidence for the decay $Ω_{c}^{0} \to π^+Ω(2012)^- \to π^+ (\bar{K}Ξ)^{-}$

Using a data sample of 980~fb$^{-1}$ collected with the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider, we present evidence for the $Ω(2012)^-$ in the resonant substructure of $Ω_{c}^{0} \to π^+ (\bar{K}Ξ)^{-}$ ($(\bar{K}Ξ)^{-}$ = $K^-Ξ^0$ + $\bar{K}^0 Ξ^-$) decays. The significance of the $Ω(2012)^-$ signal is 4.2$σ$ after considering the systematic uncertainties. The ratio of the branching fraction of $Ω_{c}^{0} \to π^{+} Ω(2012)^- \to π^+ (\bar{K}Ξ)^{-}$ relative to that of $Ω_{c}^{0} \to π^{+} Ω^-$ is calculated to be 0.220 $\pm$ 0.059(stat.) $\pm$ 0.035(syst.). The individual ratios of the branching fractions of the two isospin modes are also determined, and found to be ${\cal B}(Ω_{c}^0 \to π^+ Ω(2012)^-) \times {\cal B}(Ω(2012)^- \to K^-Ξ^0)/{\cal B}(Ω_{c}^0 \to π^+ K^- Ξ^0)$ = (9.6 $\pm$ 3.2(stat.) $\pm$ 1.8(syst.))\% and ${\cal B}(Ω_{c}^0 \to π^+ Ω(2012)^-) \times {\cal B}(Ω(2012)^- \to \bar{K}^0 Ξ^-)/{\cal B}(Ω_{c}^0 \to π^+ \bar{K}^0 Ξ^-)$ = (5.5 $\pm$ 2.8(stat.) $\pm$ 0.7(syst.))\%.

hep-ex↗

arXiv2021

Search for the dark photon in $B^0 \to A^{\prime} A^{\prime}$, $A^{\prime} \to e^+ e^-$, $μ^+ μ^-$, and $π^+ π^-$ decays at Belle

We present a search for the dark photon $A^{\prime}$ in the $B^0 \to A^{\prime} A^{\prime}$ decays, where $A^{\prime}$ subsequently decays to $e^+ e^-$, $μ^+ μ^-$, and $π^+ π^-$. The search is performed by analyzing $772 \times 10^6$ $B\overline{B}$ events collected by the Belle detector at the KEKB $e^+ e^-$ energy-asymmetric collider at the $Υ(4S)$ resonance. No signal is found in the dark photon mass range $0.01~\mathrm{GeV}/c^2 \le m_{A^{\prime}} \le 2.62~\mathrm{GeV}/c^2$, and we set upper limits of the branching fraction of $B^0 \to A^{\prime} A^{\prime}$ at the 90\% confidence level. The products of branching fractions, $\mathcal{B}(B^0 \to A^{\prime} A^{\prime}) \times \mathcal{B}(A^{\prime} \to e^+ e^-)^2$ and $\mathcal{B}(B^0 \to A^{\prime} A^{\prime}) \times \mathcal{B}(A^{\prime} \to μ^+ μ^-)^2$, have limits of the order of $10^{-8}$ depending on the $A^{\prime}$ mass. Furthermore, considering $A^{\prime}$ decay rate to each pair of charged particles, the upper limits of $\mathcal{B}(B^0 \to A^{\prime} A^{\prime})$ are of the order of $10^{-8}$-$10^{-5}$. From the upper limits of $\mathcal{B}(B^0 \to A^{\prime} A^{\prime})$, we obtain the Higgs portal coupling for each assumed dark photon and dark Higgs mass. The Higgs portal couplings are of the order of $10^{-2}$-$10^{-1}$ at $m_{h'} \simeq m_{B^0} \pm 40~\mathrm{MeV}/c^2$ and $10^{-1}$-$1$ at $m_{h'} \simeq m_{B^0} \pm 3~\mathrm{GeV}/c^2$.

hep-ex↗