arXiv subjects

T. Iijima

Publications and source records attributed to T. Iijima.

At least 37 records · Page 2Linked to original sources

arXiv2023

First measurement of the $B^{+}\toπ^{+}π^{0}π^{0}$ branching fraction and \textit{CP} asymmetry

We study $B^{+}\to π^{+}π^{0}π^{0}$ using 711 $\rm{fb}^{-1}$ of data collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. We measure an inclusive branching fraction of $(19.0\pm 1.5\pm 1.4)\times 10^{-6}$ and an inclusive \textit{CP} asymmetry of $(9.2 \pm 6.8 \pm 0.7)\%$, where the first uncertainties are statistical and the second are systematic; and a $B^{+}\to ρ(770)^{+}π^{0}$ branching fraction of $(11.2\pm 1.1\pm 0.9 ^{+0.8}_{-1.6})\times 10^{-6}$, where the third uncertainty is due to possible interference with $B^{+}\to ρ(1450)^{+}π^{0}$. We present the first observation of a structure around 1 GeV/$c^{2}$ in the $π^{0}π^{0}$ mass spectrum, with a significance of 6.4$σ$, and measure a branching fraction to be $(6.9\pm 0.9\pm 0.6)\times 10^{-6}$. We also report a measurement of local \textit{CP} asymmetry in this structure.

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arXiv2023

Search for lepton-flavor-violating $τ$ decays into a lepton and a vector meson using the full Belle data sample

Charged-lepton-flavor-violation is predicted in several new physics scenarios. We update the analysis of $τ$ lepton decays into a light charged lepton ($\ell$ = $e^{\pm}$ or $μ^{\pm}$) and a vector meson ($V^0$ = $ρ^0$, $ϕ$, $ω$, $K^{\ast0}$, or $\overline{K}{}^{\ast0}$) using 980 fb$^{-1}$ of data collected with the Belle detector at the KEKB collider. No significant excess of such signal events is observed, and thus 90% credibility level upper limits are set on the $τ\rightarrow \ell V^0$ branching fractions in the range of (1.7--$4.3) \times 10^{-8}$. These limits are improved by 30% on average from the previous results.

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arXiv2023

Search for the decay $B^0_s \rightarrow π^0 π^0$ at Belle

We report the results of the first search for the decay $B_s^0\rightarrowπ^0π^0$ using $121.4\ \rm fb^{-1}$ of data collected at the $Υ(5\rm S)$ 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 $7.7\times 10^{-6}$ on the $B_s^0\rightarrowπ^0π^0$ decay branching fraction.

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arXiv2023

Measurement of Differential Distributions of $B \to D^* \ell \bar ν_\ell$ and Implications on $|V_{cb}|$

We present a measurement of the differential shapes of exclusive $B\to D^* \ell \barν_\ell$ ($B = B^-, \bar{B}^0 $ and $\ell = e, μ$) decays with hadronic tag-side reconstruction for the full Belle data set of $711\,\mathrm{fb}^{-1}$ integrated luminosity. We extract the Caprini-Lellouch-Neubert (CLN) and Boyd-Grinstein-Lebed (BGL) form factor parameters and use an external input for the absolute branching fractions to determine the Cabibbo-Kobayashi-Maskawa matrix element and find $|V_{cb}|_\mathrm{CLN} = (40.1\pm0.9)\times 10^{-3}$ and $|V_{cb}|_\mathrm{BGL} = (40.6\pm 0.9)\times 10^{-3}$ with the zero-recoil lattice QCD point $\mathcal{F}(1) = 0.906 \pm 0.013$. We also perform a study of the impact of preliminary beyond zero-recoil lattice QCD calculations on the $|V_{cb}|$ determinations. Additionally, we present the lepton flavor universality ratio $R_{eμ} = \mathcal{B}(B \to D^* e \barν_e) / \mathcal{B}(B \to D^* μ\barν_μ) = 0.990 \pm 0.021 \pm 0.023$, the electron and muon forward-backward asymmetry and their difference $ΔA_{FB}=0.022\pm0.026\pm 0.007$, and the electron and muon $D^*$ longitudinal polarization fraction and their difference $ΔF_L^{D^*} = 0.034 \pm 0.024 \pm 0.007$. The uncertainties quoted correspond to the statistical and systematic uncertainties, respectively.

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arXiv2023

Search for rare decays $B^{+} \to D_{s}^{(\ast)+}η$, $D_{s}^{(\ast)+}\bar{K}^{0}$, $D^{+}η$, and $D^{+}K^{0}$

We present a study of rare decay modes $B^{+} \to D_{s}^{+}h^{0}$, $B^{+} \to D_{s}^{\ast+}h^{0}$, and $B^{+} \to D^{+}h^{0}$, where $h^{0}$ denotes the neutral mesons $η$ or $K^{0}$, using a data sample of $(772 \pm 10 ) \times 10^{6}$ $B\bar{B}$ events produced at the $Υ(4S)$ resonance. The data were collected by the Belle detector operating at the asymmetric-energy KEKB collider. We observe no evidence for these decays, so we provide upper limits at the 90$\%$ confidence level on the branching fractions of $B^{+} \to D_{s}^{+}h^{0}$, $D_{s}^{\ast+}h^{0}$, and $D^{+}h^{0}$ decay modes. Along with rare decay modes, we report improved measurements of the color-suppressed decay branching fractions $\mathcal{B}(\bar{B}^{0} \to D^{0}η)$ = (26.6 $\pm$ 1.2 $\pm$ 2.1) $\times$ $10^{-5}$ and $\mathcal{B}(\bar{B}^{0} \to D^{0}\bar{K}^{0})$ = (5.6 $\pm$ 0.5 $\pm$ 0.2) $\times$ $10^{-5}$. The first and second uncertainties are statistical and systematic, respectively.

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arXiv2022

Study of $B^+ \rightarrow p \overline{n} π^0$

We search for the tree-diagram dominated process $B^+ \rightarrow p \overline{n} π^0$, using a data sample of $772 \times 10^6~B\overline B$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. This is the first search with the Belle detector for a decay mode including an anti-neutron. No significant signal is observed and an $90\%$ credible upper limit on the branching fraction is set at $6.1\times10^{-6}$.

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arXiv2022

Evidence for the singly Cabibbo-suppressed decay $Ω^0_c\toΞ^-π^+$ and search for $Ω^0_c\toΞ^-K^+$ and $Ω^-K^+$ 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 for the first time the singly Cabibbo-suppressed decays $Ω^0_c\toΞ^{-}π^{+}$ and $Ω^-K^+$ and the doubly Cabibbo-suppressed decay $Ω^0_c\to Ξ^- K^{+}$. Evidence for an $Ω^0_c$ signal in the $Ω^0_c\toΞ^-π^+$ mode is reported with a significance of $4.5σ$ including systematic uncertainties. The ratio of branching fractions to the normalization mode $Ω_c^0\to Ω^-π^+$ is measured to be $${\cal B}(Ω_{c}^{0} \to Ξ^{-} π^{+} )/{\cal B}(Ω_c^0\to Ω^-π^+)=0.253\pm 0.053({\rm stat.})\pm 0.030({\rm syst.}).$$ No significant signals of $Ω^0_c\toΞ^-K^+$ and $Ω^-K^+$ modes are found. The upper limits at $90\%$ confidence level on ratios of branching fractions are determined to be $${\cal B}(Ω_{c}^{0} \to Ξ^{-} K ^{+})/{\cal B}(Ω_c^0\to Ω^-π^+) < 0.070$$ and $${\cal B}(Ω_{c}^{0} \to Ω^{-}K^{+})/{\cal B}(Ω_c^0\to Ω^-π^+) < 0.29.$$

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arXiv2022

First search for the weak radiative decays $Λ_c^+ \to Σ^+ γ$ and $Ξ_c^0 \to Ξ^0 γ$

We present the first search for the weak radiative decays $Λ_c^+ \to Σ^+ γ$ and $Ξ_c^0 \to Ξ^0 γ$ using a data sample of 980~fb$^{-1}$ collected by the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider. There are no evident $Λ_c^+ \to Σ^+ γ$ or $Ξ_c^0 \to Ξ^0 γ$ signals. Taking the decays $Λ_c^+ \to p K^- π^+$ and $Ξ_c^0 \to Ξ^- π^+$ as normalization channels, the upper limits at 90\% credibility level on the ratios of branching fractions ${\cal B}(Λ_c^+ \to Σ^+ γ)/{\cal B}(Λ_c^+ \to p K^{-} π^+) < 4.0 \times 10^{-3}$ and ${\cal B}(Ξ_c^0 \to Ξ^0 γ)/{\cal B}(Ξ_c^0 \to Ξ^- π^+) < 1.2 \times 10^{-2}$ are determined. We obtain the upper limits at 90\% credibility level on the absolute branching fractions ${\cal B}(Λ_c^+ \to Σ^+ γ) < 2.6 \times 10^{-4}$ and ${\cal B}(Ξ_c^0 \to Ξ^0 γ) < 1.8 \times 10^{-4}$.

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arXiv2022

Evidence of a new excited charmed baryon decaying to $Σ_{c}(2455)^{0,++} π^{\pm}$

We present the study of $\bar{B}^{0} \to Σ_{c}(2455)^{0,++} π^{\pm} \bar{p}$ decays based on $772\times 10^{6}$ $B\bar{B}$ events collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The $Σ_{c}(2455)^{0,++} $ candidates are reconstructed via their decay to $Λ_{c}^{+} π^{\mp}$ and $Λ_{c}^{+}$ decays to $pK^{-}π^{+},~pK_{S}^{0},$ and $Λπ^{+}$ final states. The corresponding branching fractions are measured to be ${\cal B}(\bar{B}^{0} \to Σ_{c}(2455)^{0} π^{+} \bar{p}) = (1.09 \pm 0.06 \pm 0.07)\times10^{-4}$ and ${\cal B}(\bar{B}^{0} \to Σ_{c}(2455)^{++} π^{-} \bar{p}) = (1.84\pm 0.11 \pm 0.12)\times 10^{-4}$, which are consistent with the world average values with improved precision. A new structure is found in the $M_{Σ_{c}(2455)^{0,++}π^{\pm}}$ spectrum with a significance of $4.2σ$ including systematic uncertainty. The structure is possibly an excited $Λ_{c}^{+}$ and is tentatively named $Λ_{c}(2910)^{+}$. Its mass and width are measured to be $(2913.8 \pm 5.6 \pm 3.8)$ MeV/$c^{2}$ and $(51.8\pm20.0 \pm 18.8)$ MeV, respectively. The products of branching fractions for the $Λ_{c}(2910)^{+}$ are measured to be ${\cal B}(\bar{B}^{0} \to Λ_{c}(2910)^{+}\bar{p})\times{\cal B}(Λ_{c}(2910)^{+} \to Σ_{c}(2455)^{0}π^{+}) = (9.5 \pm 3.6 \pm 1.6)\times 10^{-6}$ and ${\cal B}(\bar{B}^{0} \to Λ_{c} (2910)^{+}\bar{p})\times {\cal B}(Λ_{c}(2910)^{+} \to Σ_{c}(2455)^{++}π^{-}) = (1.24 \pm 0.35 \pm 0.10)\times 10^{-5}$. Here, the first and second uncertainties are statistical and systematic, respectively.

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arXiv2022

Measurement of the branching fractions of the $B^+ \to η\ell^+ ν_{\ell} $ and $B^+ \to η^{\prime} \ell^+ ν_{\ell} $ decays with signal-side only reconstruction in the full $q^2$ range

The branching fractions of the decays $B^{+} \to η\ell^{+} ν_{\ell}$ and $B^{+} \to η^{\prime} \ell^{+} ν_{\ell}$ are measured, where $\ell$ is either an electron or a muon, using a data sample of $711\,{\rm fb}^{-1}$ containing $772 \times 10^6 B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. To reduce the dependence of the result on the form factor model, the measurement is performed over the entire $q^2$ range. The resulting branching fractions are ${\cal B}(B^{+} \rightarrow η\ell^{+} ν_{\ell}) = (2.83 \pm 0.55_{\rm (stat.)} \pm 0.34_{\rm (syst.)}) \times 10^{-5}$ and ${\cal B}(B^{+} \rightarrow η' \ell^{+} ν_{\ell}) = (2.79 \pm 1.29_{\rm (stat.)} \pm 0.30_{\rm (syst.)}) \times 10^{-5}$.

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arXiv2022

Search for $Z^{'} \rightarrow μ^{+} μ^{-}$ in the $L_μ{-} L_τ$ gauge-symmetric model at Belle

We search for a new gauge boson $Z'$ that couples only to heavy leptons and their corresponding neutrinos in the process $e^{+} e^{-} \rightarrow Z'(\rightarrow μ^{+}μ^{-}) μ^{+}μ^{-}$, using a 643 fb$^{-1}$ data sample collected by the Belle experiment at or near the $Υ(1S,2S,3S,4S,5S)$ resonances at the KEKB collider. For the first time, effects due to initial state radiation are used in estimating the detection efficiency. No signal is observed in the mass range of 0.212 \ -- 10 GeV/${\it c}^2$ and we set an upper limit on the coupling strengh, $g'$, constraining $Z'$ as a possible contributor to the anomalous magnetic dipole moment of muon.

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arXiv2022

Search for charged lepton flavor violating decays of $Υ(1S)$

We present a search for the charged lepton-flavor-violating decays $Υ(1S)\rightarrow\ell\ell^\prime$ and radiative charged lepton-flavour-violating decays $Υ(1S)\rightarrowγ\ell\ell^\prime$ [$\ell,\ell^\prime = e, μ, τ$] using the 158 million $Υ(2S)$ sample collected by the Belle detector at the KEKB collider. This search uses $Υ(1S)$ mesons produced in $π^+π^-Υ(1S)$ transitions. We do not find any significant signal, so we provide upper limits on the branching fractions at the 90% confidence level.

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arXiv2022

An improved search for the electric dipole moment of the $τ$ lepton

We report a measurement of the electric dipole moment of the $τ$ lepton ($d_τ$) using an 833~fb$^{-1}$ data sample collected near the $Υ(4S)$ resonance, with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. Using an optimal observable method, we obtain the real and imaginary parts of $d_τ$ as ${\rm Re}(d_τ) = ( -0.62 \pm 0.63 ) \times 10^{-17} ~e{\rm cm}$ and ${\rm Im}(d_τ) = ( -0.40 \pm 0.32 ) \times 10^{-17} ~e{\rm cm}$, respectively. These results are consistent with null electric dipole moment at the present level of experimental sensitivity and improve the sensitivity by about a factor of three.

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arXiv2022

Measurement of the branching fraction and $CP$ asymmetry for $B\to\bar{D}^{0} π$ decays

We measure the branching fractions and $CP$ asymmetries for the decays $B^{0}\to \bar{D}^{0}π^{0}$ and $B^{+}\to \bar{D}^{0}π^{+}$, using a data sample of $772\times 10^{6}$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^{+}e^{-}$ collider. The branching fractions obtained and direct $CP$ asymmetries are $\mathcal{B}(B^{0}\to \bar{D}^{0}π^{0}) = [2.70 \pm 0.06~ \text{(stat.)} \pm 0.10~ \text{(syst.)}] \times 10^{-4}$, $\mathcal{B}(B^{+}\to \bar{D}^{0}π^{+}) = [4.53 \pm 0.02~ \text{(stat.)} \pm 0.15~ \text{(syst.)}] \times 10^{-3}$, $ {\cal A}_{CP}(B^{0}\to \bar{D}^{0}π^{0}) = [+0.42 \pm 2.05~ \text{(stat.)} \pm 1.22~ \text{(syst.)}]\%$, and $ {\cal A}_{CP}(B^{+}\to \bar{D}^{0}π^{+}) = [+0.19 \pm 0.36~ \text{(stat.)} \pm 0.57~ \text{(syst.)}]\%$. The measurements of $\mathcal{B}$ are the most precise to date and are in good agreement with previous results, as is the measurement of ${\cal A}_{CP}(B^{+}\to \bar{D}^{0}π^{+})$. The measurement of ${\cal A}_{CP}$ for $B^{0}\to \bar{D}^{0}π^{0}$ is the first for this mode, and the value is consistent with Standard Model expectations.

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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

The study of $γγ\toγψ(2S)$ at Belle

Using $980~\rm fb^{-1}$ of data on and around the $Υ(nS)(n=1,2,3,4,5)$ resonances collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider, the two-photon process $γγ\to γψ(2S)$ is studied from the threshold to $4.2~{\rm GeV}$ for the first time. Two structures are seen in the invariant mass distribution of $γψ(2S)$: one at $M_{R_1} = 3922.4\pm 6.5 \pm 2.0~{\rm MeV}/c^2$ with a width of $Γ_{R_1} = 22\pm 17\pm 4~{\rm MeV}$, and another at $M_{R_2} = 4014.3\pm 4.0 \pm 1.5~{\rm MeV}/c^2$ with a width of $Γ_{R_2} = 4\pm 11 \pm 6~{\rm MeV}$; the signals are parametrized with the incoherent sum of two Breit-Wigner functions. The first structure is consistent with the $X(3915)$ or the $χ_{c2}(3930)$, and the local statistical significance is determined to be $3.1σ$ with the systematic uncertainties included. The second matches none of the known charmonium or charmoniumlike states, and its global significance is determined to be $2.8σ$ including the look-elsewhere effect. The production rates are $Γ_{γγ}{\cal B}(R_1\toγψ(2S)) = 9.8\pm 3.6\pm 1.2~{\rm eV}$ assuming $(J^{PC}, |λ|) =(0^{++}, 0)$ or $2.0\pm 0.7\pm 0.2~{\rm eV}$ with $(2^{++}, 2)$ for the first structure and $Γ_{γγ}{\cal B}(R_2\toγψ(2S)) = 6.2\pm 2.2\pm 0.8~{\rm eV}$ with $(0^{++}, 0)$ or $1.2\pm 0.4\pm 0.2~{\rm eV}$ with $(2^{++}, 2)$ for the second one. Here, the first errors are statistical and the second systematic, and $λ$ is the helicity.

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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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