A xi hyperon that carries a unit negative charge designated Ξ-; also known as "cascade particle".

A hyperon is a comparatively massive baryon that may be unstable or partially stable and is short-lived.

A baryon is a subatomic particle belonging to a group that undergoes strong interactions, has a mass greater than or equal to that of the proton (a stable, positively charged elementary particle), and consists of three quarks.