Search for $B^0$ meson decays into $\Lambda$ and missing energy with a hadronic tagging method at Belle

TL;DR

This paper searches for rare $B^0$ meson decays into a $ ext{Lambda}$ baryon and missing energy using a large data sample from Belle, setting the most restrictive upper limits to date with implications for baryogenesis and dark matter.

Contribution

First search for $B^0$ decays into $ ext{Lambda}$ and missing energy using hadronic tagging at Belle, establishing new upper limits on branching fractions.

Findings

No evidence for the decays was observed.

Set 90% CL upper limits on branching fractions between 2.1 and 3.8 x 10^{-5}.

Provides the most restrictive limits to date.

Abstract

We present a search for the decays of $B^0$ mesons into a final state containing a $\Lambda$ baryon and missing energy. These results are obtained from a $711\text{fb}^{-1}$ data sample that contains $772 \times 10^6$ $B{\kern 0.18em}\overline{\kern -0.18em B}$ pairs and was collected near the $\Upsilon(4S)$ resonance with the Belle detector at the KEKB asymmetric-energy $e^+e^-$ collider. We use events in which one $B$ meson is fully reconstructed in a hadronic decay mode and require the remainder of the event to consist of only a single $\Lambda$. No evidence for these decays is found and we set $90\%$ confidence level upper limits on the branching fractions in the range $2.1$-$3.8\times 10^{-5}$. This measurement provides the world's most restrictive limits, with implications for baryogenesis and dark matter production.