The pion is a semistable meson produced either in a neutral form with a mass 264 times that of an electron and a mean lifetime of 8.4 × 10-17 seconds, or in a positively or negatively charged form with a mass 273 times that of an electron and a mean lifetime of 2.6 × 10-8 seconds.

It is also called a pi-meson (π-meson).

The π-meson is a meson involved in holding the nucleus together - it was initially considered to be the exchange particle for the strong nuclear force, but now the gluon is considered responsible for that.

It is produced as the result of high-energy particle collision - cosmic rays interacting in the upper atmosphere result in pion production.

It can also be produced when the Sigma ⁺ baryon decays via the weak interaction.

Decay processes:

- negatively charged ones decay into a muon and a muon antineutrino by weak interaction

- positively charged ones decay into an anti-muon and a muon neutrino by weak interaction

- the uncharged pion decays to an electron, positron, and gamma ray by the electromagnetic interaction

Lifetimes:

• The neutral pions have a lifetime of about 10^-16 seconds.
• The positive and negative pions have longer lifetimes of about 2.6 x 10^-8 seconds.