# Rare hyperon decays with missing energy

## TL;DR

This paper investigates hyperon decays with missing energy, analyzing standard model predictions and potential new physics effects, highlighting scenarios where new physics could significantly enhance decay rates within experimental reach.

## Contribution

It provides a model-independent analysis of hyperon decays with missing energy, identifying conditions under which new physics could notably increase decay rates beyond standard model expectations.

## Key findings

- Standard model predicts branching fractions below 10^{-11}
- Parity-odd new physics operators can significantly enhance decay rates
- Enhanced decay rates could be observable in ongoing experiments like BESIII

## Abstract

We explore the strangeness-changing decays of the lightest hyperons into another baryon plus missing energy within and beyond the standard model (SM). In the SM these processes arise from the loop-induced quark transition $s\to d\nu\bar\nu$ and their branching fractions are estimated to be less than $10^{-11}$. In the presence of new physics (NP) the rates of these hyperon decays with missing energy could increase significantly with respect to the SM expectations because of modifications to the SM process or contributions from additional modes with new invisible particles. Adopting a model-independent approach and taking into account constraints from the kaon sector, we find that the current data on $K\to\pi\nu\bar\nu$ do not permit sizable NP impact on the hyperon decays via underlying operators having mainly parity-even quark parts. In contrast, NP operators with primarily parity-odd quark parts are much less restricted by the existing bounds on $K\to\rm invisible$ and $K\to\pi\pi\nu\bar\nu$ and consequently could produce substantially amplifying effects on the hyperon modes. Their NP-enhanced branching fractions could reach levels potentially observable in the ongoing BESIII experiment.