arXiv subjects

T. Kumita

Publications and source records attributed to T. Kumita.

At least 55 records · Page 3Linked to original sources

arXiv2016

First model-independent Dalitz analysis of $B^0 \to DK^{*0}$, $D\to K_S^0π^+π^-$ decay

We report a measurement of the amplitude ratio $r_S$ of $B^0 \to D^0K^{*0}$ and $B^0 \to \bar{D^0}K^{*0}$ decays with a Dalitz analysis of $D\to K_S^0π^+π^-$ decays, for the first time using a model-independent method. We set an upper limit $r_S < 0.87$ at the 68\% confidence level, using the full data sample of $772\times10^6$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB $e^+e^-$ collider. This result is obtained from observables $x_- = +0.4 ^{+1.0 +0.0}_{-0.6 -0.1} \pm0.0$, $y_- = -0.6 ^{+0.8 +0.1}_{-1.0 -0.0} \pm0.1$, $x_+ = +0.1 ^{+0.7 +0.0}_{-0.4 -0.1} \pm0.1$ and $y_+ = +0.3 ^{+0.5 +0.0}_{-0.8 -0.1} \pm0.1$, where $x_\pm = r_S \cos(δ_S \pm ϕ_3)$, $y_\pm = r_S \sin(δ_S \pm ϕ_3)$ and $ϕ_3~(δ_S)$ is the weak (strong) phase difference between $B^0 \to D^0K^{*0}$ and $B^0 \to \bar{D^0}K^{*0}$.

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arXiv2016

Study of $π^0$ pair production in single-tag two-photon collisions

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.

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arXiv2016

Measurement of the Lepton Forward-Backward Asymmetry in $B \rightarrow X_s \ell^+ \ell^-$ Decays with a Sum of Exclusive Modes

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.

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arXiv2015

First Observation of the Decay B0->psi(2S)pi0

We report a measurement of the $B^0\rightarrowψ(2S)π^0$ branching fraction based on the full $Υ(4S)$ data set of $772\times10^{6}$ $B\bar{B}$ pairs collected by the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We obtain $B(B^0\rightarrowψ(2S)π^0) = (1.17\pm0.17\text{(stat)}\pm0.08\text{(syst)})\times10^{-5}$. The result has a significance of 7.2 standard deviations and is the first observation of the decay $B^0\rightarrowψ(2S)π^0$.

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arXiv2015

Search for the rare decay $D^0\toγγ$ at Belle

We search for the rare radiative decay $D^0\toγγ$ using a data sample with an integrated luminosity of $832{\rm fb^{-1}}$ recorded by the Belle detector at the KEKB $e^+e^-$ asymmetric-energy collider. We find no statistically significant signal and set an upper limit on the branching fraction of ${\cal B}(D^0\toγγ)<8.5\times10^{-7}$ at $90\%$ confidence level. This is the most restrictive limit on the decay channel to date.

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arXiv2015

Observation of $B^{0} \rightarrow p\barΛ D^{(*)-}$

We report the first observation of the decays $B^0 \rightarrow p\barΛ D^{(*)-}$. The data sample of $711$ fb$^{-1}$ used in this analysis corresponds to $772$ million $B\bar{B}$ pairs, collected at the $Υ(4S)$ resonance by the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. We observe $19.8σ$ and $10.8σ$ excesses of events for the two decay modes and measure the branching fractions of $B^0 \rightarrow p\barΛ D^{-}$ and $B^0 \rightarrow p\barΛ D^{*-}$ to be $(25.1\pm2.6\pm3.5)\times10^{-6}$ and $(33.6\pm6.3\pm4.4)\times10^{-6}$, respectively, where the first uncertainties are statistical and the second are systematic. These results are not compatible with the predictions based on the generalized factorization approach. In addition, a threshold enhancement in the di-baryon ($p\barΛ$) system is observed, consistent with that observed in similar $B$ decays.

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arXiv2015

Semi-inclusive studies of semileptonic $B_s$ decays at Belle

We present an analysis of the semi-inclusive decays $B_s \to D_s^- X \ell^+ ν$ and $B_s \to D_s^{*-} X \ell^+ ν$, where $X$ denotes a final state that may consist of additional hadrons or photons and $\ell$ is an electron or muon. The studied $B_s$ decays are contained in the $121.4~{\rm fb}^{-1}$ $Υ(5S)$ data sample collected by the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The branching fractions of the decays are measured to be $\mathcal{B}(B_s \to D_s^- X \ell^+ ν) = [8.2 \pm 0.2 (\text{stat}) \pm 0.6 (\text{syst}) \pm 1.4 (\text{ext})]\%$ and $\mathcal{B}(B_s \to D_s^{*-} X \ell^+ ν) = [5.4 \pm 0.4 (\text{stat}) \pm 0.4 (\text{syst}) \pm 0.9 (\text{ext})]\%$, where the first two uncertainties are statistical and systematic and the last is due to external parameters. The measurement also provides an estimate of the $B_s^{(*)}\bar{B}_s^{(*)}$ production cross-section, $σ(e^+e^- \to B_s^{(*)}\bar{B}_s^{(*)}) = (53.8 \pm 1.4 (\text{stat}) \pm 4.0 (\text{syst}) \pm 3.4 (\text{ext}))\,{\rm pb}$, at the center-of-mass energy $\sqrt{s} = 10.86\,{\rm GeV}$.

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arXiv2015

Measurements of $B\rightarrow \bar{D} D_{s0} ^{+}(2317)$ decay rates and a search for isospin partners of the $D_{s0}^{+} (2317)$

We report improved measurements of the product branching fractions ${\mathcal B}(B^+\rightarrow\bar{D}^0 D_{s0}^{*+} (2317))\times{\mathcal B}( D_{s0} ^{*+}(2317)\rightarrow D_s^{+}π^0) =(8.0^{+1.3}_{-1.2} \pm 1.1 \pm 0.4)\times 10^{-4}$ and ${\mathcal B}(B^0\rightarrow D^- D_{s0} ^{*+}(2317))\times{\mathcal B}(D_{s0}^{*+}(2317)\rightarrow D_s^{+}π^0) =(10.2^{+1.3}_{-1.2} \pm 1.0 \pm 0.4)\times 10^{-4}$, where the first errors are statistical, the second are systematic and the third are from $D$ and $D_s$ branching fractions. In addition, we report negative results from a search for hypothesized neutral ($Z^0$) and doubly charged ($Z^{++}$) isospin partners of the $D_{s0}^{*+}(2317)$ and provide upper limits on the product branching fractions ${\mathcal B}(B^0 \rightarrow D^0 z^0)\times{\mathcal B}(z^0\rightarrow D_s^{+}π^-)$ and ${\mathcal B}(B^+\rightarrow D^- z^{++})\times{\mathcal B}(z^{++}\rightarrow D_s^{+}π^+)$ that are more than an order of magnitude smaller than theoretical expectations for the hypotheses that the $D_{s0} ^{*+}(2317)$ is a member of an isospin triplet. The analysis uses a 711 fb$^{-1}$ data sample containing 772 million $B\bar{B}$ meson pairs collected at the $Υ(4S)$ resonance in the Belle detector at the KEKB collider.

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arXiv2015

Evidence for the decay B0->eta pi^0

We report a search for the charmless hadronic decay $B^0\toηπ^0$ with a data sample corresponding to an integrated luminosity of 694 $\rm fb^{-1}$ containing $753\times10^6$ $B\bar{B}$ pairs. The data were collected by the Belle experiment running on the $Υ(4S)$ resonance at the KEKB $e^+e^-$ collider. We measure a branching fraction $\mathcal{B}(B^0\toηπ^0)=(4.1^{+1.7+0.5}_{-1.5-0.7})\times 10^{-7}$, where the first uncertainty is statistical and the second is systematic. Our measurement gives an upper limit of $\mathcal{B}(B^0\toηπ^0)<6.5\times 10^{-7}$ at 90\% confidence level. The signal has a significance of $3.0$ standard deviations and constitutes the first evidence for this decay mode.

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arXiv2015

First observation of the hadronic transition $ Υ(4S) \to ηh_{b}(1P)$ and new measurement of the $h_b(1P)$ and $η_b(1S)$ parameters

Using a sample of $771.6 \times 10^{6}$ $Υ(4S)$ decays collected by the Belle experiment at the KEKB $e^+e^-$ collider, we observe for the first time the transition $Υ(4S) \to ηh_b(1P)$ with the branching fraction ${\cal B}[Υ(4S) \to ηh_b(1P)]= (2.18 \pm 0.11 \pm 0.18) \times 10^{-3}$ and we measure the $h_b(1P)$ mass $M_{h_{b}(1P)} = (9899.3 \pm 0.4 \pm 1.0)$ MeV/$c^{2}$, corresponding to the hyperfine splitting $ΔM_{\mathrm HF}(1P) = (0.6 \pm 0.4 \pm 1.0)$ MeV/$c^{2}$. Using the transition $h_b(1P) \to γη_b(1S)$, we measure the $η_b(1S)$ mass $M_{η_{b}(1S)} = (9400.7 \pm 1.7 \pm 1.6)$ MeV/$c^{2}$, corresponding to $ΔM_{\mathrm HF}(1S) = (59.6 \pm 1.7 \pm 1.6)$ MeV/$c^{2}$, the $η_b(1S)$ width $Γ_{η_{b}(1S)} = (8 ^{+6}_{-5} \pm 5)$ MeV/$c^{2}$ and the branching fraction ${\cal B}[h_b(1P) \to γη_b(1S)]= (56 \pm 8 \pm 4) \%$.

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arXiv2015

Measurement of the direct $CP$ asymmetry in $\bar{B}\rightarrow X_{s+d}γ$ decays with a lepton tag

We report the measurement of the direct $CP$ asymmetry in the radiative $\bar{B}\rightarrow X_{s+d}γ$ decay using a data sample of $(772 \pm 11)\times 10^6$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The $CP$ asymmetry is measured as a function of the photon energy threshold. For $E^{\rm{*}}_γ \geq 2.1~{\rm{GeV}}$, where $E^{\rm{*}}_γ$ is the photon energy in the center-of-mass frame, we obtain $\mathcal{A}_{CP}(\bar{B}\rightarrow X_{s+d}γ)= (2.2 \pm 3.9 \pm 0.9) \%$, consistent with the Standard Model prediction.

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arXiv2015

Search for B+ -> l+ nu gamma decays with hadronic tagging using the full Belle data sample

We search for the decay B+ -> l+ nu gamma with l+ = e+ or mu+ using the full Belle data set of 772 x 10^6 BBbar pairs, collected at the Y(4S) resonance with the Belle detector at the KEKB asymmetric-energy e+e- collider. We reconstruct one B meson in a hadronic decay mode and search for the B+ -> l+ nu gamma decay in the remainder of the event. We observe no significant signal within the phase space of E_gamma^sig > 1 GeV and obtain upper limits of BR(B+ -> e+ nu gamma) < 6.1 x 10^-6, BR(B+ -> mu+ nu gamma) < 3.4 x 10^-6, and BR(B+ -> l+ nu gamma) < 3.5 x 10^-6 at 90 % credibility level.

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arXiv2014

Measurement of Time-Dependent $CP$ Violation in $B^0\to η'K^0$ Decays

We present a measurement of the time-dependent $CP$ violation parameters in $B^0\toη'K^0$ decays. The measurement is based on the full data sample containing $772\times 10^6$ $B\bar{B}$ pairs collected at the $Υ(4S)$ resonance using the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. The measured values of the mixing-induced and direct $CP$ violation parameters are: \begin{align} \sin 2 ϕ^{\rm eff}_1 &= +0.68\pm 0.07 \pm 0.03, \nonumber \\ \mathcal{A}_{η'K^0} &= +0.03\pm 0.05\pm 0.04, \nonumber \end{align} where the first uncertainty is statistical and the second is systematic. The values obtained are the most accurate to date. Furthermore, these results are consistent with our previous measurements and with the world-average value of $\sin 2ϕ_1$ measured in $B^0\to J/ψK^0$ decays.}

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arXiv2014

Measurement of $B^0 \to D_s^- K^0_Sπ^+$ and $B^+ \to D_s^- K^+K^+$ branching fractions

We report a measurement of the $B^0$ and $B^+$ meson decays to the $D_s^-K^0_S π^+$ and $D_s^- K^+K^+$ final states, respectively, using $657 \times 10^{6} B\overline{B}$ pairs collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. Using the $D_s^-\to ϕπ^-$, $K^{*}(892)^0 K^-$ and $K^0_S K^-$ decay modes for the $D_s$ reconstruction, we measure the following branching fractions: ${\cal B}(B^0\to D_s^{-}K^0_Sπ^+)=[0.47 \pm 0.06 (\mathrm {stat}) \pm 0.05 (\mathrm {syst})]\times 10^{-4}$ and ${\cal B}(B^+\to D_s^-K^+K^+)= [0.93 \pm 0.22 (\mathrm {stat})\pm 0.10 (\mathrm {syst})]\times 10^{-5}$. We find the ratio of the branching fraction of $B^+\to D_s^-K^+K^+$ to that of the analogous Cabibbo favored $B^+\to D_s^-K^+π^+$ decay to be ${\cal R}_{\cal B} = 0.054 \pm 0.013 ({\rm stat}) \pm 0.006 ({\rm syst})$, which is consistent with the na\"ıve factorization model. We also observe a deviation from the three-body phase-space model for both studied decays.

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arXiv2014

Measurement of the inclusive semileptonic branching fraction $\mathcal{B}(B_s^0 \rightarrow X^- \ell^+ ν_\ell)$ at Belle

We report a measurement of the inclusive semileptonic $B_s^0$ branching fraction in a $121~fb^{-1}$ data sample collected near the $Υ(5S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^+ e^-$ collider. Events containing $B_s^0$ pairs are selected by reconstructing a tag side $D_s^+$ and identifying a signal side lepton $\ell^+$ ($\ell = e, μ$) that is required to have the same-sign charge to ensure that both originate from different $B_s^0$ mesons. The $B_s^0 \rightarrow X^- \ell^+ ν_\ell$ branching fraction is extracted from the ratio of the measured yields of $D_s^+$ mesons and $D_s^+ \ell^+$ pairs and the known production and branching fractions. The inclusive semileptonic branching fraction is measured to be $[9.6 \pm 0.4\text{(stat)} \pm 0.7\text{(syst)}]~\%$.

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arXiv2014

Observation of $e^+e^- \to π^+ π^- π^0 χ_{bJ}$ and search for $X_b \to ωΥ(1S)$ at $\sqrt{s}\sim 10.867$ GeV

The $e^+e^- \to π^+ π^- π^0 χ_{bJ}$ ($J=0,~1,~2$) processes are studied using a 118~fb$^{-1}$ data sample collected at a center-of-mass energy of 10.867 GeV, in the $Υ(10860)$ energy range, with the Belle detector. The $π^+ π^- π^0 χ_{b1}$, $π^+π^-π^0χ_{b2}$, $ωχ_{b1}$ signals and the evidence of $ωχ_{b2}$ are observed for the first time and the cross sections are measured. No significant $π^+π^-π^0χ_{b0}$ or $ωχ_{b0}$ signal is observed and 90\% confidence level upper limits on the cross sections for these two processes are obtained. In the $π^+π^-π^0$ invariant mass spectrum, significant non-$ω$ signals are also observed. We search for the $X(3872)$-like state with a hidden $b\bar{b}$ component (named $X_b$) decaying into $ωΥ(1S)$; no significant signal is observed with a mass between $10.55$ and $10.65$ GeV/$c^2$.

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arXiv2014

Observation of the decay $B^0 \to η' K^*(892)^0$

We report a search for charmless hadronic decays of neutral $B$ mesons to $η' K^{*}(892)^{0}$. The results are based on a 711fb$^{-1}$ data sample that contains $772\times 10^6 B\overline{B}$ pairs, collected at the $Υ(4S)$ resonance with the Belle detector at the KEKB asymmetric energy $e^+e^-$ collider. We observe the decay for the first time with a significance of 5.0 standard deviations and obtain its branching fraction ${\cal B}[B^0\toη' K^{*}(892)^{0}]=[2.6\pm0.7{\rm (stat)}\pm0.2{\rm (syst)}]\times 10^{-6}$. We also measure the $CP$ violating asymmetry as ${\cal A}_{CP}[B^0\toη' K^{*}(892)^{0}]=-0.22\pm0.29{\rm (stat)}\pm0.07{\rm syst}$.

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arXiv2014

Measurement of the Branching Fraction Br(Lambda_c+ -> p K- pi+)

We present the first model-independent measurement of the absolute branching fraction of the Lambda_c+ -> p K- pi+ decay using a data sample of 978 fb^-1 collected with the Belle detector at the KEKB asymmetric-energy e+e- collider. The number of Lambda_c+ baryons is determined by reconstructing the recoiling D(*)- anti-p pi+ system in events of the type e+e- -> D(*)- anti-p pi+ Lambda_c+. The branching fraction is measured to be Br(Lambda_c+ -> p K- pi+) = (6.84 +- 0.24^{+0.21}_{-0.27})%, where the first and second uncertainties are statistical and systematic, respectively.

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