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Register a new userSearch for $B^{-}tomu^{-}bar u_mu$ Decays at the Belle Experiment
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We report the result of a search for the decay $B^{-}tomu^{-}bar u_mu$. The signal events are selected based on the presence of a high momentum muon and the topology of the rest of the event showing properties of a generic $B$-meson decay, as well as the missing energy and momentum being consistent with the hypothesis of a neutrino from the signal decay. We find a 2.4 standard deviation excess above background including systematic uncertainties, which corresponds to a branching fraction of ${cal B}(B^{-}tomu^{-}bar u_mu) =(6.46 pm 2.22 pm 1.60 )times10^{-7}$ or a frequentist 90% confidence level interval on the $B^{-}tomu^{-}bar u_mu$ branching fraction of $[2.9, 10.7]times 10^{-7}$. This result is obtained from a $711 text{fb}^{-1}$ data sample that contains $772 times 10^6$ $Bbar{B}$ pairs, collected near the $Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+ e^-$ collider.
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This contribution illustrates a new search for the flavor-changing neutral-current decay ${B^+ to K^+ u bar u}$ performed by the Belle II experiment at the SuperKEKB asymmetric-energy electron-positron collider. In this study, a sample corresponding to an integrated luminosity of $63, rm{fb}^{-1}$ collected at the $rm Upsilon(4S)$ resonance and an additional sample of $9, rm{fb}^{-1}$ collected at an energy $60, rm MeV$ below the resonance are used. A novel technique, based on an inclusive tagging method and exploiting the topological features of the ${B^+ to K^+ u bar u}$ decay, is employed and it provides a higher signal efficiency with respect to the methods used in the previous searches. No significant signal is observed. An upper limit of $4.1 times 10^{-5}$ is set on the ${B^+ to K^+ u bar u}$ branching fraction at the $90, %$ confidence level.
The MiniBooNE experiment at Fermilab reports results from an analysis of $bar u_e$ appearance data from $11.27 times 10^{20}$ protons on target in antineutrino mode, an increase of approximately a factor of two over the previously reported results. An event excess of $78.4 pm 28.5$ events ($2.8 sigma$) is observed in the energy range $200<E_ u^{QE}<1250$ MeV. If interpreted in a two-neutrino oscillation model, $bar{ u}_{mu}rightarrowbar{ u}_e$, the best oscillation fit to the excess has a probability of 66% while the background-only fit has a $chi^2$-probability of 0.5% relative to the best fit. The data are consistent with antineutrino oscillations in the $0.01 < Delta m^2 < 1.0$ eV$^2$ range and have some overlap with the evidence for antineutrino oscillations from the Liquid Scintillator Neutrino Detector (LSND). All of the major backgrounds are constrained by in-situ event measurements so non-oscillation explanations would need to invoke new anomalous background processes. The neutrino mode running also shows an excess at low energy of $162.0 pm 47.8$ events ($3.4 sigma$) but the energy distribution of the excess is marginally compatible with a simple two neutrino oscillation formalism. Expanded models with several sterile neutrinos can reduce the incompatibility by allowing for CP violating effects between neutrino and antineutrino oscillations.
The first dedicated search for the $eta_{c2}(1D)$ is carried out using the decays $B^+ rightarrow eta_{c2}(1D) K^+$, $B^0 rightarrow eta_{c2}(1D) K^0_S$, $B^0 rightarrow eta_{c2}(1D) pi^- K^+$, and $B^+ rightarrow eta_{c2}(1D) pi^+ K^0_S$ with $eta_{c2}(1D) to h_c gamma$. No significant signal is found. For the $eta_{c2}(1D)$ mass range between $3795$ and $3845 mathrm{MeV}/c^2$, the branching-fraction upper limits are determined to be $mathcal{B}(B^+ rightarrow eta_{c2}(1D) K^+) times mathcal{B}(eta_{c2}(1D) to h_c gamma) < 3.7 times 10^{-5}$, $mathcal{B}(B^0 rightarrow eta_{c2}(1D) K^0_S) times mathcal{B}(eta_{c2}(1D) to h_c gamma) < 3.5 times 10^{-5}$, $mathcal{B}(B^0 rightarrow eta_{c2}(1D) pi^- K^+) times mathcal{B}(eta_{c2}(1D) to h_c gamma) < 1.0 times 10^{-4}$, and $mathcal{B}(B^+ rightarrow eta_{c2}(1D) pi^+ K^0_S) times mathcal{B}(eta_{c2}(1D) to h_c gamma) < 1.1 times 10^{-4}$ at 90% C. L. The analysis is based on the 711 $mathrm{fb}^{-1}$ data sample collected on the $Upsilon(4S)$ resonance by the Belle detector, which operated at the KEKB asymmetric-energy $e^+ e^-$ collider.
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 $mathcal{B},(B^0torm{invisible}+gamma) < 1.6times10^{-5}$.
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