69 research outputs found

    Test of lepton flavor universality with measurements of R(D+)R(D^{+}) and R(D+)R(D^{*+}) using semileptonic BB tagging at the Belle II experiment

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    International audienceWe report measurements of the ratios of branching fractions R(D()+)=B(B0D()+τντ)B(B0D()+ν){\cal R}(D^{(*)+}) = \frac{{\cal B}(\overline{B}{}^0 \to D^{(*)+} \,τ^- \, \overlineν_τ)}{{\cal B}(\overline{B}{}^0 \to D^{(*)+} \, \ell^- \, \overlineν_\ell)}, where \ell denotes either an electron or a muon. These ratios test the universality of the charged-current weak interaction. The results are based on a 365fb1365\, \mathrm{fb}^{-1} data sample collected with the Belle II detector at the SuperKEKB e+ee^+e^- collider, which operates at a center-of-mass energy corresponding to the Υ(4S)Υ(4S) resonance, just above the threshold for BBB\overline{B}{} production. Signal candidates are reconstructed by selecting events in which the companion BB meson from the Υ(4S)BBΥ(4S) \to B\overline{B}{} decay is identified in semileptonic modes. The ττ lepton is reconstructed via its leptonic decays. We obtain R(D+)=0.418±0.074 (stat)±0.051 (syst){\cal R}(D^+) = 0.418 \pm 0.074 ~({\mathrm{stat}}) \pm 0.051 ~({\mathrm{syst}}) and R(D+)=0.306±0.034 (stat)±0.018 (syst){\cal R}(D^{*+}) = 0.306 \pm 0.034 ~({\mathrm{stat}}) \pm 0.018 ~({\mathrm{syst}}), which are consistent with world average values. Accounting for the correlation between them, these values differ from the Standard Model expectation by a collective significance of 1.71.7 standard deviations

    Measurement of the D0Kπ+e+e D^{0}\rightarrow K^{-}π^{+}e^{+}e^{-} branching fraction and search for D0π+πe+e D^{0}\rightarrow π^{+}π^{-}e^{+}e^{-} and D0K+Ke+eD^{0}\rightarrow K^{+}K^{-}e^{+}e^{-} decays at Belle

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    International audienceWe present a study of the rare charm meson decays D0K+Ke+e D^{0}\rightarrow K^{+}K^{-}e^{+}e^{-} , π+πe+e π^{+}π^{-}e^{+}e^{-} , and Kπ+e+e K^{-}π^{+}e^{+}e^{-} using a 942 fb1^{-1} data set collected by the Belle detector at the KEKB asymmetric-energy e+e e^{+}e^{-} collider. We use D0 D^{0} candidates identified by the charge of the pion in DD0π D^{*} \rightarrow D^{0} π decays and normalize the branching fractions to D0Kπ+ππ+ D^{0} \rightarrow K^{-}π^{+}π^{-}π^{+} decays. The branching fraction for decay D0Kπ+e+e D^{0} \rightarrow K^{-}π^{+}e^{+}e^{-} is measured to be (39.6 ±\pm 4.5 (stat) ±\pm 2.9 (syst)) ×\times 10710^{-7}, with the dielectron mass in the ρ/ω ρ/ω mass region 675<mee<875 675 < m_{ee} < 875 MeV/c2/c^{2}. We also search for D0hh()+e+e D^{0}\rightarrow h^{-} h^{(\prime)+}e^{+}e^{-} (h()=K,π h^{(\prime)}=K,\,π) decays with the dielectron mass near the ηη and ϕϕ resonances, and away from these resonances for the K+Ke+e K^{+}K^{-}e^{+}e^{-} and π+πe+e π^{+}π^{-}e^{+}e^{-} modes. For these modes, we find no significant signals and set 90%\% confidence level upper limits on their branching fractions at the O\mathcal{O}(107^{-7}) level

    Measurement of the time-integrated CPCP asymmetry in D0π0π0D^0\to\pi^0\pi^0 decays at Belle II

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    We measure the time-integrated CPCP asymmetry, ACPA_{CP}, in D0π0π0D^0\to\pi^0\pi^0 decays reconstructed in e+eccˉe^+e^-\to c\bar{c} events collected by Belle II during 2019--2022. The data corresponds to an integrated luminosity of 428fb1\mathrm{fb}^{-1}. The D0D^0 decays are required to originate from the flavor-conserving D+D0π+D^{*+} \to D^0 \pi^+ decay to determine the charm flavor at production time. Control samples of D0Kπ+D^0\to K^- \pi^+ decays, with or without an associated pion from a D+D^{*+} decay, are used to correct for detection asymmetries. The result, ACP(D0π0π0)=(0.30±0.72±0.20)%A_{CP}(D^0\to\pi^0\pi^0) = (0.30\pm 0.72\pm 0.20)\%, where the first uncertainty is statistical and the second systematic, is consistent with CPCP symmetry

    Measurement of the time-integrated CP asymmetry in D0KS0KS0D^{0}\rightarrow K^{0}_{S}K^{0}_{S} decays using Belle and Belle II data

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    We measure the time-integrated CP asymmetry in D0KS0KS0D^{0} \rightarrow K^{0}_{S}K^{0}_{S} decays reconstructed in e+ecce^{+}e^{-} \rightarrow c\overline{c} events collected by the Belle and Belle II experiments. The corresponding data samples have integrated luminosities of 980 fb1^{-1} and 428 fb1^{-1}, respectively. The D0D^{0} decays are required to originate from the D+D0π+D^{*+} \rightarrow D^{0}\pi^{+} decay, which determines the charm flavor at production time. A control sample of D0K+KD^{0} \rightarrow K^{+}K^{-} decays is used to correct for production and detection asymmetries. The result, (1.4±1.3(stat)±0.1(syst))%(-1.4\pm1.3{\rm(stat)}\pm0.1{\rm (syst)})\%, is consistent with previous determinations and with CP symmetry

    Measurement of the inclusive branching fractions for Bs0{B}_{s}^{0} decays into D mesons via hadronic tagging

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    Abstract We report measurements of the absolute branching fractions B(Bs0Ds±X)\mathcal{B}\left({B}_{s}^{0}\to {D}_{s}^{\pm }X\right) , B(Bs0D0/D0X)\mathcal{B}\left({B}_{s}^{0}\to {D}^{0}/{\overline{D} }^{0}X\right) , and B(Bs0D±X)\mathcal{B}\left({B}_{s}^{0}\to {D}^{\pm }X\right) , where the latter is measured for the first time. The results are based on a 121.4 fb −1 data sample collected at the Υ(10860) resonance by the Belle detector at the KEKB asymmetric-energy e + e − collider. We reconstruct one Bs0{B}_{s}^{0} meson in e+eΥ(10860)BsBs{e}^{+}{e}^{-}\to \Upsilon\left(10860\right)\to {B}_{s}^{*}{\overline{B} }_{s}^{*} events and measure yields of Ds+{D}_{s}^{+} , D 0, and D + mesons in the rest of the event. We obtain B(Bs0Ds±X)=(68.6±7.2±4.0)%\mathcal{B}\left({B}_{s}^{0}\to {D}_{s}^{\pm }X\right)=\left(68.6\pm 7.2\pm 4.0\right)\% , B(Bs0D0/D0X)=(21.5±6.1±1.8)%\mathcal{B}\left({B}_{s}^{0}\to {D}^{0}/{\overline{D} }^{0}X\right)=\left(21.5\pm 6.1\pm 1.8\right)\% , and B(Bs0D±X)=(12.6±4.6±1.3)%\mathcal{B}\left({B}_{s}^{0}\to {D}^{\pm }X\right)=\left(12.6\pm 4.6\pm 1.3\right)\% , where the first uncertainty is statistical and the second is systematic. Averaging with previous Belle measurements gives B(Bs0Ds±X)=(63.4±4.5±2.2)%\mathcal{B}\left({B}_{s}^{0}\to {D}_{s}^{\pm }X\right)=\left(63.4\pm 4.5\pm 2.2\right)\% and B(Bs0D0/D0X)=(23.9±4.1±1.8)%\mathcal{B}\left({B}_{s}^{0}\to {D}^{0}/{\overline{D} }^{0}X\right)=\left(23.9\pm 4.1\pm 1.8\right)\% . For the Bs0{B}_{s}^{0} production fraction at the Υ(10860), we find fs=(21.41.7+1.5)%{f}_{s}=\left({21.4}_{-1.7}^{+1.5}\right)\%

    Measurement of the time-integrated CPCP asymmetry in D0KS0KS0D^0 \to K^0_{\rm S} K^0_{\rm S} decays using opposite-side flavor tagging at Belle and Belle II

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    We measure the time-integrated CPCP asymmetry in D0KS0KS0D^0 \to K^0_{\rm S} K^0_{\rm S} decays reconstructed in e+ecce^+e^-\to c{\overline c} events collected by the Belle and Belle II experiments. The corresponding data samples have integrated luminosities of 980 and 428 fb1{}^{-1}, respectively. To infer the flavor of the D0D^0 meson, we exploit the correlation between the flavor of the reconstructed decay and the electric charges of particles reconstructed in the rest of the e+ecce^+e^-\to c{\overline c} event. This results in a sample which is independent from any other previously used at Belle or Belle II. The result, ACP(D0KS0KS0)=(1.3±2.0±0.2)%A_{CP}(D^0 \to K^0_{\rm S} K^0_{\rm S}) = (1.3 \pm 2.0 \pm 0.2)\%, where the first uncertainty is statistical and the second systematic, is consistent with previous determinations and with CPCP symmetry

    Determination of |Vcb| using B -> D l nu decays at Belle II

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    Model-independent measurement of D0D^0-D0\overline{D}{}^0 mixing parameters in D0KS0π+πD^0\rightarrow K^0_{S}\pi^+\pi^- decays at Belle and Belle II

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    We perform a model-independent measurement of the D0D^0-D0\overline{D}{}^0 mixing parameters using samples of e+ee^+e^--collision data collected by the Belle and Belle II experiments that have integrated luminosities of 951 fb1951\ \text{fb}^{-1} and 408 fb1408\ \text{fb}^{-1}, respectively. Approximately 2.05×1062.05\times10^6 neutral DD mesons are reconstructed in the D0KS0π+πD^0\rightarrow K^0_{S}\pi^+\pi^- channel, with the neutral DD flavor tagged by the charge of the pion in the D+D0π+D^{*+}\rightarrow D^0\pi^+ decay. Assuming charge-parity symmetry, the mixing parameters are measured to be x=(4.0±1.7±0.4)×103 x = (4.0\pm1.7\pm0.4)\times 10^{-3} and y=(2.9±1.4±0.3)×103 y = (2.9\pm1.4\pm0.3)\times 10^{-3}, where the first uncertainties are statistical and the second systematic. The results are consistent with previous determinations

    Model-independent measurement of D0D^0-D0\overline{D}{}^0 mixing parameters in D0KS0π+πD^0\rightarrow K^0_{S}\pi^+\pi^- decays at Belle and Belle II

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    We perform a model-independent measurement of the D0D^0-D0\overline{D}{}^0 mixing parameters using samples of e+ee^+e^--collision data collected by the Belle and Belle II experiments that have integrated luminosities of 951 fb1951\ \text{fb}^{-1} and 408 fb1408\ \text{fb}^{-1}, respectively. Approximately 2.05×1062.05\times10^6 neutral DD mesons are reconstructed in the D0KS0π+πD^0\rightarrow K^0_{S}\pi^+\pi^- channel, with the neutral DD flavor tagged by the charge of the pion in the D+D0π+D^{*+}\rightarrow D^0\pi^+ decay. Assuming charge-parity symmetry, the mixing parameters are measured to be x=(4.0±1.7±0.4)×103 x = (4.0\pm1.7\pm0.4)\times 10^{-3} and y=(2.9±1.4±0.3)×103 y = (2.9\pm1.4\pm0.3)\times 10^{-3}, where the first uncertainties are statistical and the second systematic. The results are consistent with previous determinations

    Model-independent measurement of D0D^0-D0\overline{D}{}^0 mixing parameters in D0KS0π+πD^0\rightarrow K^0_{S}\pi^+\pi^- decays at Belle and Belle II

    No full text
    International audienceWe perform a model-independent measurement of the D0D^0-D0\overline{D}{}^0 mixing parameters using samples of e+ee^+e^--collision data collected by the Belle and Belle II experiments that have integrated luminosities of 951 fb1951\ \text{fb}^{-1} and 408 fb1408\ \text{fb}^{-1}, respectively. Approximately 2.05×1062.05\times10^6 neutral DD mesons are reconstructed in the D0KS0π+πD^0\rightarrow K^0_{S}\pi^+\pi^- channel, with the neutral DD flavor tagged by the charge of the pion in the D+D0π+D^{*+}\rightarrow D^0\pi^+ decay. Assuming charge-parity symmetry, the mixing parameters are measured to be x=(4.0±1.7±0.4)×103 x = (4.0\pm1.7\pm0.4)\times 10^{-3} and y=(2.9±1.4±0.3)×103 y = (2.9\pm1.4\pm0.3)\times 10^{-3}, where the first uncertainties are statistical and the second systematic. The results are consistent with previous determinations
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