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Register a new userSearch for $D^{0}$ decays to invisible final states at Belle
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We report the result from the first search for $D^0$ decays to invisible final states. The analysis is performed on a data sample of 924 $rm{fb}^{-1}$ collected at and near the $Upsilon(4S)$ and $Upsilon(5S)$ resonances with the Belle detector at the KEKB asymmetric-energy $e^{+}e^{-}$ collider. The absolute branching fraction is determined using an inclusive $D^0$ sample, obtained by fully reconstructing the rest of the particle system including the other charmed particle. No significant signal yield is observed and an upper limit of $9.4times 10^{-5}$ is set on the branching fraction of $D^0$ to invisible final states at 90% confidence level.
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We report a search for $B^{0}$ decays into invisible final states using a data sample of $657 times 10^{6}$ $Bbar{B}$ pairs collected at the $Upsilon(4S)$ resonance with the Belle detector at the KEKB $e^{+}e^{-}$ collider. The signal is identified by fully reconstructing a hadronic decay of the accompanying $B$ meson and requiring no other particles in the event. No significant signal is observed, and we obtain an upper limit of $1.3 times 10^{-4}$ at the 90% confidence level for the branching fraction of invisible $B^{0}$ decay.
We report searches for $B^0torm{invisible}$ and $B^0torm{invisible}+gamma$ decays, where the energy of the photon is required to be larger than 0.5 GeV. These results are obtained from a $711,{rm fb}^{-1}$ data sample that contains $772 times 10^6 Bbar{B}$ pairs and was collected near the $Upsilon,(4S)$ resonance with the Belle detector at the KEKB $e^+ e^-$ collider. We observe no significant signal for either decay and set upper limits on their branching fractions at $90%$ confidence level of $mathcal{B},(B^0torm{invisible}) < 7.8times10^{-5}$ and $mathcal{B},(B^0torm{invisible}+gamma) < 1.6times10^{-5}$.
A search for mixing in the neutral D meson system has been performed using semileptonic D0 -> K(*)- e+ u and D0 -> K(*)- mu+ u decays. Neutral D mesons from D*+ -> D0 pi_s^+ decays are used and the flavor at production is tagged by the charge of the slow pion. The measurement is performed using 492 fb^-1 of data recorded by the Belle detector. From the yield of right-sign and wrong-sign decays arising from non-mixed and mixed events, respectively, we measure the ratio of the time-integrated mixing rate to the unmixed rate to be R_M = (1.3 +- 2.2 +- 2.0) x 10^-4. This corresponds to an upper limit of R_M < 6.1 x 10^-4 at the 90% C.L.
We present the results of the first Dalitz plot analysis of the decay $D^{0}to K^{-}pi^{+}eta$. The analysis is performed on a data set corresponding to an integrated luminosity of 953 $rm{fb}^{-1}$ collected by the Belle detector at the asymmetric-energy $e^{+}e^{-}$ KEKB collider. The Dalitz plot is well described by a combination of the six resonant decay channels $bar{K}^{*}(892)^0eta$, $K^{-}a_0(980)^+$, $K^{-}a_2(1320)^+$, $bar{K}^{*}(1410)^0eta$, $K^{*}(1680)^-pi^{+}$ and $K_2^{*}(1980)^-pi^{+}$, together with $Kpi$ and $Keta$ S-wave components. The decays $K^{*}(1680)^{-}to K^{-}eta$ and $K_{2}^{*}(1980)^{-}to K^{-}eta$ are observed for the first time. We measure ratio of the branching fractions, $frac{mathcal{B}(D^{0}to K^{-}pi^{+}eta)}{mathcal{B}(D^{0}to K^{-}pi^{+})}=0.500pm0.002{rm(stat)}pm0.020{rm(syst)}pm0.003{rm (mathcal{B}_{PDG})}$. Using the Dalitz fit result, the ratio $frac{mathcal{B}(K^{*}(1680)to Keta)}{mathcal{B}(K^{*}(1680)to Kpi)}$ is measured to be $0.11pm0.02{rm(stat)}^{+0.06}_{-0.04}{rm(syst)}pm0.04{rm(mathcal{B}_{text{PDG}})}$; this is much lower than the theoretical expectations ($approx1$) made under the assumption that $K^{*}(1680)$ is a pure $1^{3}D_1$ state. The product branching fraction $mathcal{B}(D^0to [K_2^{*}(1980)^-to K^{-}eta]pi^{+})=(2.2^{+1.7}_{-1.9})times10^{-4}$ is determined. In addition, the $pieta^{prime}$ contribution to the $a_0(980)^{pm}$ resonance shape is confirmed with 10.1$sigma$ statistical significance using the three-channel Flatt{e} model. We also measure $mathcal{B}(D^0tobar{K}^{*}(892)^0eta)=(1.41^{+0.13}_{-0.12})%$. This is consistent with, and more precise than, the current world average $(1.02pm0.30)%$, deviates with a significance of more than $3sigma$ from the theoretical predictions of (0.51-0.92)%.
We have searched for neutrinoless $tau$ lepton decays into $ell$ and $V^0$, where $ell$ stands for an electron or muon, and $V^0$ for a vector meson ($phi$, $omega$, $K^{*0}$, $bar{K}^{*0}$ or $rho^0$), using 543 fb$^{-1}$ of data collected with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. No excess of signal events over the expected background has been observed, and we set upper limits on the branching fractions in the range $(5.9-18) times 10^{-8}$ at the 90% confidence level. These upper limits include the first results for the $ell omega$ mode as well as new limits that are significantly more restrictive than our previous results for the $ell phi$, $ell K^{*0}$, $ell bar{K}^{*0}$ and $ell rho^0$ modes.
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