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Abstract
We report searches for $B^0\to\rm{invisible}$ and $B^0\to\rm{invisible}+\gamma$ 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 $772 \times 10^6 B\bar{B}$ 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 $\mathcal{B}\,(B^0\to\rm{invisible}) < 7.8\times10^{-5}$ and $\mathcal{B}\,(B^0\to\rm{invisible}+\gamma) < 1.6\times10^{-5}$.
Highlights
We observe no significant signal for either decay and set upper limits on their branching fractions at 90% confidence level of BðB0 → invisibleÞ < 7.8 × 10−5 and BðB0 → invisible þ γÞ < 1.6 × 10−5
The decays B0 → invisible and B0 → invisible þ γ, with “invisible” defined as particles that leave no signal in the Belle detector, are sensitive to new physics beyond the Standard Model (SM)
Models with R-parity violation [1] or dark matter contributions [2] predict that the branching fraction of B0 decays to an invisible final state could be as high as 10−6 − 10−7
Summary
We report searches for B0 → invisible and B0 → invisible þ γ decays, where the energy of the photon is required to be larger than 0.5 GeV These results are obtained from a 711 fb−1 data sample that contains 772 × 106BBpairs and was collected near the Υð4SÞ resonance with the Belle detector at the KEKB eþe− collider. The decays B0 → invisible and B0 → invisible þ γ, with “invisible” defined as particles that leave no signal in the Belle detector, are sensitive to new physics beyond the Standard Model (SM). Comparing to the full reconstruction algorithm used in the previous B0 → invisible study at Belle [7], the tagging efficiency is improved by approximately a factor of 1.5 due to the newly introduced NN tool within the framework In this analysis, a loose preselection on the beam-energyconstrained Btag mass, Mbc;tag > 5.26qGffiffieffiffiVffiffiffiffi=ffifficffiffiffi2ffiffi,ffiffiiffiffisffiffiffiaffiffipffiffiffipffiffilied. For B0 → invisible þ γ, the signal photon is excluded in all the momentum-related calculations in order to reduce model
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