arXiv subjects
Publications and source records attributed to E. Kato.
We report on a search for heavy neutrinos in B-meson decays. The results are obtained using a data sample that contains 772x10^6 BB-bar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. No signal is observed and upper limits are set on mixing of heavy neutrinos with left-handed neutrinos of the Standard Model in the mass range 0.5 - 5.0 GeV/c^2.
We report a search for $B$ decays to selected final states with the $η_c$ meson: $B^{\pm}\to K^{\pm}η_cπ^+π^-$, $B^{\pm}\to K^{\pm}η_cω$, $B^{\pm}\to K^{\pm}η_cη$ and $B^{\pm}\to K^{\pm}η_cπ^0$. The analysis is based on $772\times 10^6$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We set 90\% confidence level upper limits on the branching fractions of the studied $B$ decay modes, independent of intermediate resonances, in the range $(0.6-5.3)\times 10^{-4}$. We also search for molecular-state candidates in the $D^0\bar{D}^{*0}-\bar{D}^0D^{*0}$, $D^0\bar{D}^0+\bar{D}^0D^0$ and $D^{*0}\bar{D}^{*0}+\bar{D}^{*0}D^{*0}$ combinations, neutral partners of the $Z(3900)^{\pm}$ and $Z(4020)^{\pm}$, and a poorly understood state $X(3915)$ as possible intermediate states in the decay chain, and set 90\% confidence level upper limits on the product of branching fractions to the mentioned intermediate states and decay branching fractions of these states in the range $(0.6-6.9)\times 10^{-5}$.
We present a measurement of the branching fraction and the longitudinal polarization fraction of $B^{0}\rightarrowρ^+ρ^-$ decays, as well as the time-dependent $CP$ violating parameters in decays into longitudinally polarized $ρ^{+}ρ^{-}$ pairs with Belle's final data set of $772\times 10^6$ $B\bar{B}$ pairs, at the $Υ(4S)$ resonance, collected at the asymmetric-energy $e^+ e^-$ collider KEKB. We obtain ${\cal B}(B^0 \rightarrow ρ^+ ρ^-)=(28.3\pm 1.5\;(\rm stat) \pm 1.5\;(\rm syst))\times 10^{-6}$, $f_L = 0.988\pm 0.012\;(\rm stat ) \pm0.023\;(\rm syst)$, ${\cal A}_{CP} = 0.00\pm0.10\;(\rm stat ) \pm0.06\;(\rm syst)$, ${\cal S}_{CP} = -0.13\pm0.15\;(\rm stat ) \pm0.05\;(\rm syst).$ We perform an isospin analysis to constrain the CKM angle $ϕ_2$ and obtain two solutions with \begin{eqnarray} ϕ_{2} = (93.7\pm10.6)^{\circ},\nonumber \end{eqnarray} being most compatible with other Standard-Model based fits to the data.
We report new measurements of the total cross sections for $e^+e^-\to Υ(n{\rm S})π^+π^-$ ($n$ = 1, 2, 3) and $e^+e^-\to b\bar b$ from a high-luminosity fine scan of the region $\sqrt{s} = 10.63$-$11.05$ GeV with the Belle detector. We observe that the $Υ(n{\rm S})π^+π^-$ spectra have little or no non-resonant component and extract from them the masses and widths of $Υ(10860)$ and $Υ(11020)$ and their relative phase. We find $M_{10860}=(10891.1\pm3.2^{+0.6}_{-1.7})$ MeV/$c^2$ and $Γ_{10860}=(53.7^{+7.1}_{-5.6}\,^{+1.3}_{-5.4})$ MeV and report first measurements $M_{11020}=(10987.5^{+6.4}_{-2.5}\,^{+9.0}_{-2.1})$ MeV/$c^2$, $Γ_{11020}=(61^{+9}_{-19}\,^{+2}_{-20})$ MeV, and $ϕ_{\rm 11020}-ϕ_{\rm 10860} = (-1.0\pm0.4\,^{+1.4}_{-0.1})$ rad.
Using a data sample of 980 ${\rm fb}^{-1}$ of $e^+e^-$ annihilation data taken with the Belle detector operating at the KEKB asymmetric-energy $e^+e^-$ collider, we report the results of a study of excited $Ξ_c$ states that decay, via the emission of photons and/or charged pions, into $Ξ_c^0$ or $Ξ_c^+$ ground state charmed-strange baryons. We present new measurements of the masses of all members of the $Ξ_c^{\prime}$, $Ξ_c(2645)$, $Ξ_c(2790)$, $Ξ_c(2815)$, and $Ξ_c(2980)$ isodoublets, measurements of the intrinsic widths of those that decay strongly, and evidence of previously unknown transitions.
We report measurement of the cross section of $e^+e^-\to π^+π^-ψ(2S)$ between 4.0 and $5.5 {\rm GeV}$, based on an analysis of initial state radiation events in a $980 \rm fb^{-1}$ data sample recorded with the Belle detector. The properties of the $Y(4360)$ and $Y(4660)$ states are determined. Fitting the mass spectrum of $π^+π^-ψ(2S)$ with two coherent Breit-Wigner functions, we find two solutions with identical mass and width but different couplings to electron-positron pairs: $M_{Y(4360)} = (4347\pm 6\pm 3) {\rm MeV}/c^2$, $Γ_{Y(4360)} = (103\pm 9\pm 5) {\rm MeV}$, $M_{Y(4660)} = (4652\pm10\pm 8) {\rm MeV}/c^2$, $Γ_{Y(4660)} = (68\pm 11\pm 1) \rm MeV$; and ${\cal{B}}[Y(4360)\to π^+π^-ψ(2S)]\cdot Γ_{Y(4360)}^{e^+e^-} = (10.9\pm 0.6\pm 0.7) \rm eV$ and ${\cal{B}}[Y(4660)\to π^+π^-ψ(2S)]\cdot Γ_{Y(4660)}^{e^+e^-} = (8.1\pm 1.1\pm 0.5) \rm eV$ for one solution; or ${\cal{B}}[Y(4360)\to π^+π^-ψ(2S)]\cdot Γ_{Y(4360)}^{e^+e^-} = (9.2\pm 0.6\pm 0.6) \rm eV$ and ${\cal{B}}[Y(4660)\to π^+π^-ψ(2S)]\cdot Γ_{Y(4660)}^{e^+e^-} = (2.0\pm 0.3\pm 0.2) \rm eV$ for the other. Here, the first errors are statistical and the second systematic. Evidence for a charged charmoniumlike structure at $4.05 {\rm GeV}/c^2$ is observed in the $π^{\pm}ψ(2S)$ intermediate state in the $Y(4360)$ decays.
We report the discovery of $Ξ_{c}(3055)^{0}$, observed by its decay into the final state $ΛD^{0}$, and present the first observation and evidence of the decays of $Ξ_c(3055)^{+}$ and $Ξ_c(3080)^{+}$ into $ΛD^{+}$. We also perform a combined analysis of the $ΛD^{+}$ with the $Σ_{c}^{++}K^{-}$ and $Σ_{c}^{\ast ++}K^{-}$ decay modes to measure the ratios of branching fractions, masses and widths with improved accuracy. We measure the ratios of branching fractions ${\cal B}(Ξ_{c}(3055)^{+} \to ΛD^{+})/{\cal B}(Ξ_{c}(3055)^{+} \to Σ_{c}^{++}K^{-})=5.09\pm1.01\pm0.76$, ${\cal B}(Ξ_{c}(3080)^{+} \to ΛD^{+})/{\cal B}(Ξ_{c}(3080)^{+} \to Σ_{c}^{++}K^{-})=1.29\pm0.30\pm0.15$, and ${\cal B}(Ξ_{c}(3080)^{+} \to Σ_{c}^{\ast ++}K^{-})/{\cal B}(Ξ_{c}(3080)^{+} \to Σ_{c}^{++}K^{-})=1.07\pm0.27\pm0.01$, where the uncertainties are statistical and systematic. The analysis is performed using a 980 fb$^{-1}$ data sample collected with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider.
We present a search for a non-Standard-Model invisible particle $X^0$ in the mass range $0.1\textrm{-}1.8 \,{\rm GeV}/{c^2}$ in $B^{+}\to e^{+} X^{0}$ and $B^{+}\to μ^{+} X^{0}$ decays. The results are obtained from a $711~{\rm fb}^{-1}$ data sample that corresponds to $772 \times 10^{6} B\bar{B}$ pairs, collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. One $B$ meson is fully reconstructed in a hadronic mode to determine the momentum of the lepton of the signal decay in the rest frame of the recoiling partner $B$ meson. We find no evidence of a signal and set upper limits on the order of $10^{-6}$.
We measure the decay $B_s^0\rightarrow K^0\overline{K}^0$ using data collected at the $Υ(5S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. The data sample used corresponds to an integrated luminosity of 121.4 ${\rm fb^{-1}}$. We measure a branching fraction $\mathcal{B}(B_s^0\rightarrow K^0\overline{K}^0) = [19.6\,^{+5.8}_{-5.1}({\rm stat.})\,\pm1.0({\rm sys.})\,\pm 2.0(N^{}_{B_s^0\overline{B}_s^0})]\times 10^{-6}$ with a significance of 5.1 standard deviations. This measurement constitutes the first observation of this decay.
The process $γγ\to p \bar{p} K^+ K^-$ and its intermediate processes are measured for the first time using a 980~fb$^{-1}$ data sample collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The production of $p \bar{p} K^+ K^-$ and a $Λ(1520)^0~(\barΛ(1520)^0)$ signal in the $pK^-$~($\bar{p} K^+$) invariant mass spectrum are clearly observed. However, no evidence for an exotic baryon near 1540~MeV/$c^2$, denoted as $Θ(1540)^0$~($\barΘ~(1540)^0$) or $Θ(1540)^{++}$~($Θ(1540)^{--}$), is seen in the $p K^-$~($\bar{p}K^+$) or $pK^+$~($\bar{p} K^-$) invariant mass spectra. Cross sections for $γγ\to p \bar{p} K^+ K^-$, $Λ(1520)^0 \bar{p} K^+ +c.c.$ and the products $σ(γγ\to Θ(1540)^0 \bar{p} K^+ +c.c.)\BR(Θ(1540)^0 \to p K^{-})$ and $σ(γγ\to Θ(1540)^{++} \bar{p} K^- +c.c.)\BR(Θ(1540)^{++}\to p K^{+})$ are measured. We also determine upper limits on the products of the $χ_{c0}$ and $χ_{c2}$ two-photon decay widths and their branching fractions to $p \bar{p} K^+ K^-$ at the 90\% credibility level.
We report inclusive and exclusive measurements for $χ_{c1}$ and $χ_{c2}$ production in $B$ decays. We measure $\mathcal{B}(B \to χ_{c1} X)$= $(3.03 \pm 0.05(\mbox{stat}) \pm 0.24(\mbox{syst})) \times 10^{-3}$ and $\mathcal{B}(B \to χ_{c2} X)$= $(0.70 \pm 0.06(\mbox{stat}) \pm 0.10(\mbox{syst})) \times 10^{-3}$. For the first time, $χ_{c2}$ production in exclusive $B$ decays in the modes $B^0 \to χ_{c2}π^- K^+$ and $B^+ \to χ_{c2} π^+ π^- K^+$ has been observed, along with first evidence for the $B^+ \to χ_{c2} π^+ K_S^0$ decay mode. For $χ_{c1}$ production, we report the first observation in the $B^+ \to χ_{c1} π^+ π^- K^+$, $B^0 \to χ_{c1} π^+ π^- K_S^0$ and $B^0 \to χ_{c1} π^0 π^- K^+$ decay modes. Using these decay modes, we observe a difference in the production mechanism of $χ_{c2}$ in comparison to $χ_{c1}$ in $B$ decays. In addition, we report searches for $X(3872)$ and $χ_{c1}(2P)$ in the $B^+ \to (χ_{c1} π^+ π^-) K^+$ decay mode. The reported results use $772 \times 10^{6}$ $B\overline{B}$ events collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider.
We have searched for the decay B0 -> phi gamma using the full Belle data set of 772 x 10^6 BBbar pairs collected at the Upsilon(4S) resonance with the Belle detector at the KEKB e+e- collider. No signal is observed, and we set an upper limit on the branching fraction of B(B0 -> phi gamma) < 1.0 x 10^{-7} at 90% confidence level. This is the most stringent limit on this decay mode to date.
We report a measurement of the differential cross section of $π^0$ pair production in single-tag two-photon collisions, $γ^* γ\to π^0 π^0$, in $e^+ e^-$ scattering. The cross section is measured for $Q^2$ up to 30 GeV$^2$, where $Q^2$ is the negative of the invariant mass squared of the tagged photon, in the kinematic range 0.5 GeV < W < 2.1 GeV and $|\cos θ^*|$ < 1.0 for the total energy and pion scattering angle, respectively, in the $γ^* γ$ center-of-mass system. The results are based on a data sample of 759 fb$^{-1}$ collected with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. The transition form factor of the $f_0(980)$ and that of the $f_2(1270)$ with the helicity-0, -1, and -2 components separately are measured for the first time and are compared with theoretical calculations.
We search for the process $B^0 \to π^- τ^+ ν_τ$ using the full Belle data set of $711\,{\rm fb}^{-1}$, corresponding to $772 \times 10^6 B\bar{B}$ pairs, collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider. We reconstruct one $B$ meson in a hadronic decay and search for the $B^0 \to π^- τ^+ ν_τ$ process in the remainder of the event. No significant signal is observed and an upper limit of $\mathcal{B}(B^0 \to π^- τ^+ ν_τ) < 2.5 \times 10^{-4}$ is obtained at the $90\%$ confidence level.
We report the first measurement of the lepton forward-backward asymmetry ${\cal A}_{\rm FB}$ as a function of the squared four-momentum of the dilepton system, $q^2$, for the electroweak penguin process $B \rightarrow X_s \ell^+ \ell^-$ with a sum of exclusive final states, where $\ell$ is an electron or a muon and $X_s$ is a hadronic recoil system with an $s$ quark. The results are based on a data sample containing $772\times10^6$ $B\bar{B}$ pairs recorded at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. ${\cal A}_{\rm FB}$ for the inclusive $B \rightarrow X_s \ell^+ \ell^-$ is extrapolated from the sum of 10 exclusive $X_s$ states whose invariant mass is less than 2 GeV/$c^2$. For $q^2 > 10.2$ GeV$^2$/$c^2$, ${\cal A}_{\rm FB} < 0$ is excluded at the 2.3$σ$ level, where $σ$ is the standard deviation. For $q^2 < 4.3$ GeV$^2$/$c^2$, the result is within 1.8$σ$ of the Standard Model theoretical expectation.
We present a determination of the magnitude of the Cabibbo-Kobayashi-Maskawa matrix element $|V_{cb}|$ using the decay $B\to D\ellν_\ell$ ($\ell=e,μ$) based on 711 fb$^{-1}$ of $e^+e^-\to Υ(4S)$ data recorded by the Belle detector and containing $772 \times 10^6$ $B\bar{B}$ pairs. One $B$ meson in the event is fully reconstructed in a hadronic decay mode while the other, on the signal side, is partially reconstructed from a charged lepton and either a $D^+$ or $D^0$ meson in a total of 23 hadronic decay modes. The isospin-averaged branching fraction of the decay $B\to D\ellν_\ell$ is found to be $\mathcal{B}(B^0 \to D^- \ell^+ ν_{\ell})=(2.31\pm 0.03(\mathrm{stat})\pm 0.11(\mathrm{syst}))\%$. Analyzing the differential decay rate as a function of the hadronic recoil with the parameterization of Caprini, Lelouch and Neubert and using the form-factor prediction $\mathcal{G}(1)=1.0541\pm 0.0083$ calculated by FNAL/MILC, we obtain $η_\mathrm{EW}|V_{cb}|=(40.12\pm 1.34)\times 10^{-3}$, where $η_\mathrm{EW}$ is the electroweak correction factor. Alternatively, assuming the model-independent form-factor parameterization of Boyd, Grinstein and Lebed and using lattice QCD data from the FNAL/MILC and HPQCD collaborations, we find $η_\mathrm{EW}|V_{cb}|=(41.10 \pm 1.14)\times 10^{-3}$.
We report the analysis of the three-body e+e- => B B-bar pi, B B*-bar pi, and B* B*-bar pi processes, including the first observation of the Zb+-(10610) =>[B B*-bar+c.c.]+- and Zb+-(10650) => [B*B*-bar]+- transitions. We measure visible cross sections for the three-body production of sigma_vis(e+e- => [B B*-bar+c.c.]+-pi-+=(11.2+-1.0(stat.)+-1.2(syst.)) pb and sigma_vis(e+e- => [B*B*-bar]+-pi-+)=(5.61+-0.73(stat.)+-0.66(syst.)) pb and set a 90% C.L. upper limit of sigma_vis(e+e- => [BB-bar]+-pi-+)<2.1 pb. The results are based on a 121.4 1/fb data sample collected with the Belle detector at a center-of-mass energy near the Y(5S) peak.
We report the first observation of the decay $Λ^{+}_{c} \rightarrow p K^{+} π^{-}$ using a 980 $\mathrm{fb^{-1}}$ data sample collected by the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. This is the first doubly Cabibbo-suppressed decay of a charmed baryon to be observed. We measure the branching ratio of this decay with respect to its Cabibbo-favored counterpart to be $\mathcal{B}(Λ^{+}_{c} \rightarrow p K^{+} π^{-})/\mathcal{B}(Λ^{+}_{c} \rightarrow p K^{-} π^{+})=(2.35\pm0.27\pm0.21)\times10^{-3}$, where the uncertainties are statistical and systematic, respectively.