What is "pions"

Usage examples of "pions".

And when a proton annihilates an antiproton, it produces a pi-zero meson one-third of the time, and a charged pion, a muon, and a neutrino two-thirds of the time, after which the pions and neutrons promptly break down to electrons and positrons, photons and neutrinos.

Actually, that makes sense: neutrons decaying into protons and pions would transmute some of the calcium to scandium, the oxygen to fluorine, and the carbon to nitrogen.

The electrons make gamma rays, and the nuclei make pions, all high energy stuff.