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Register a new userSearch for $B^{0}$ decays to invisible final states at Belle
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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.
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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 $mathcal{B},(B^0torm{invisible}+gamma) < 1.6times10^{-5}$.
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.
We report on the first measurement of the direct $CP$-violating asymmetry ($mathcal{A}$) in the charmless decay $B^0 to K^0pi^0$ at Belle II and an updated measurement of its branching fraction ($mathcal{B}$). We use a sample of electron-positron collisions collected in 2019 and 2020 at the $Upsilon(4S)$ resonance and corresponding to $62.8$ $text{fb}^{-1}$ of integrated luminosity. We reconstruct and select about $50$ $B^0 to K_S^0 pi^0$ candidates, and we measure $mathcal{A}_{{K^0pi^0}} = -0.40_{-0.44}^{+0.46} (text{stat}) pm 0.04 (text{syst})$ and $mathcal{B}(B^0 to K^0 pi^0) = [8.5_{-1.6}^{+1.7} (text{stat}) pm 1.2 (text{syst})] times 10^{-6}$. This is the first measurement of $CP$ violation in $B^0 to K^0pi^0$ decays reported by Belle II. The results agree with previous determinations and show a detector performance comparable with the best Belle results.
We report a search for $B$ decays to selected final states with the $eta_c$ meson: $B^{pm}to K^{pm}eta_cpi^+pi^-$, $B^{pm}to K^{pm}eta_comega$, $B^{pm}to K^{pm}eta_ceta$ and $B^{pm}to K^{pm}eta_cpi^0$. The analysis is based on $772times 10^6$ $Bbar{B}$ pairs collected at the $Upsilon(4S)$ 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 $D^0bar{D}^{*0}-bar{D}^0D^{*0}$, $D^0bar{D}^0+bar{D}^0D^0$ 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 search for a non-Standard-Model invisible particle $X^0$ in the mass range $0.1textrm{-}1.8 ,{rm GeV}/{c^2}$ in $B^{+}to e^{+} X^{0}$ and $B^{+}to mu^{+} X^{0}$ decays. The results are obtained from a $711~{rm fb}^{-1}$ data sample that corresponds to $772 times 10^{6} Bbar{B}$ pairs, collected at the $Upsilon(4S)$ 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 $10^{-6}$.
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