The exchange of virtual pions, along with vector, rho and omega mesons, provides an explanation for the residual strong force between nucleons.

Pions are not produced in radioactive decay, but commonly are in high-energy collisions between hadrons.

In 2013, the detection of characteristic gamma rays originating from the decay of neutral pions in two supernova remnants has shown that pions are produced copiously after supernovas, most probably in conjunction with production of high-energy protons that are detected on Earth as cosmic rays.

[citation needed] Theoretical work by Hideki Yukawa in 1935 had predicted the existence of mesons as the carrier particles of the strong nuclear force.

From the range of the strong nuclear force (inferred from the radius of the atomic nucleus), Yukawa predicted the existence of a particle having a mass of about 100 MeV/c2.

In 1947, the first true mesons, the charged pions, were found by the collaboration led by Cecil Powell at the University of Bristol, in England.

The discovery article had four authors: César Lattes, Giuseppe Occhialini, Hugh Muirhead and Powell.

Photographic emulsions based on the gelatin-silver process were placed for long periods of time in sites located at high-altitude mountains, first at Pic du Midi de Bigorre in the Pyrenees, and later at Chacaltaya in the Andes Mountains, where the plates were struck by cosmic rays.

After development, the photographic plates were inspected under a microscope by a team of about a dozen women.

[4] Marietta Kurz was the first person to detect the unusual "double meson" tracks, characteristic for a pion decaying into a muon, but they were too close to the edge of the photographic emulsion and deemed incomplete.

A few days later, Irene Roberts observed the tracks left by pion decay that appeared in the discovery paper.

In 1948, Lattes, Eugene Gardner, and their team first artificially produced pions at the University of California's cyclotron in Berkeley, California, by bombarding carbon atoms with high-speed alpha particles.

Further advanced theoretical work was carried out by Riazuddin, who in 1959 used the dispersion relation for Compton scattering of virtual photons on pions to analyze their charge radius.

Neutral pions do not leave tracks in photographic emulsions or Wilson cloud chambers.

The existence of the neutral pion was inferred from observing its decay products from cosmic rays, a so-called "soft component" of slow electrons with photons.

The π0 was identified definitively at the University of California's cyclotron in 1949 by observing its decay into two photons.

... Yukawa choose the letter π because of its resemblance to the Kanji character for 介 [kai], which means "to mediate".

Due to the concept that the meson works as a strong force mediator particle between hadrons.

[7]The use of pions in medical radiation therapy, such as for cancer, was explored at a number of research institutions, including the Los Alamos National Laboratory's Meson Physics Facility, which treated 228 patients between 1974 and 1981 in New Mexico,[8] and the TRIUMF laboratory in Vancouver, British Columbia.

In the standard understanding of the strong force interaction as defined by quantum chromodynamics, pions are loosely portrayed as Goldstone bosons of spontaneously broken chiral symmetry.

If their current quarks were massless particles, it could make the chiral symmetry exact and thus the Goldstone theorem would dictate that all pions have a zero mass.

The pion is one of the particles that mediate the residual strong interaction between a pair of nucleons.

The π± mesons have a mass of 139.6 MeV/c2 and a mean lifetime of 2.6033×10−8 s. They decay due to the weak interaction.

This implies that the lepton must be emitted with spin in the direction of its linear momentum (i.e., also right-handed).

[12] Although this explanation suggests that parity violation is causing the helicity suppression, the fundamental reason lies in the vector-nature of the interaction which dictates a different handedness for the neutrino and the charged lepton.

The rate at which pions decay is a prominent quantity in many sub-fields of particle physics, such as chiral perturbation theory.

This rate is parametrized by the pion decay constant (fπ), related to the wave function overlap of the quark and antiquark, which is about 130 MeV.

[13] The π0 meson has a mass of 135.0 MeV/c2 and a mean lifetime of 8.5×10−17 s.[1] It decays via the electromagnetic force, which explains why its mean lifetime is much smaller than that of the charged pion (which can only decay via the weak force).

The neutral pion has also been observed to decay into positronium with a branching fraction on the order of 10−9.

The branching fractions above are the PDG central values, and their uncertainties are omitted, but available in the cited publication.