Hyperon Physics at BESIII

TL;DR

The BESIII experiment used spin polarization and entanglement to study hyperon-antihyperon pairs, observing significant polarization effects and enabling precise tests of CP-violation in hyperon decays, complementing kaon decay studies.

Contribution

This work provides the first independent measurements of decay parameters for hyperons and antihyperons, utilizing polarization data to test CP-violation with unprecedented precision.

Findings

Significant transverse polarization observed in hyperon decays.

First independent determination of decay parameters for hyperons and antihyperons.

Precise tests of direct CP-violation in hyperon decays.

Abstract

Spin polarization and entanglement are utilized by the BESIII experiment to learn more about the production and decay properties of hyperon-antihyperon pairs in a series of recent analyses of its unprecedented datasets at the $J/\psi$ and $\psi'$ resonances. This has lead to the observation of significant transverse polarisation in decays of $J/\psi$ or $\psi'$ into $\Lambda \bar{\Lambda}$, $\Sigma \bar{\Sigma}$, $\Xi \bar{\Xi}$, and $\Omega \bar{\Omega}$. Because of the non-zero polarization, the decay parameters for the most common hadronic weak decays of both hyperons and antihyperons could be determined independently for the first time. Comparing these to each other yields precise tests of direct, $\Delta S = 1$ CP-violation that complement measurements of kaon decays.