Hadron

Almost all "free" hadrons and antihadrons (meaning, in isolation and not bound within an atomic nucleus) are believed to be unstable and eventually decay into other particles.

The only known possible exception is free protons, which appear to be stable, or at least, take immense amounts of time to decay (order of 1034+ years).

A similar process occurs in the natural environment, in the extreme upper-atmosphere, where muons and mesons such as pions are produced by the collisions of cosmic rays with rarefied gas particles in the outer atmosphere.

[6] The term "hadron" is a new Greek word introduced by L. B. Okun in a plenary talk at the 1962 International Conference on High Energy Physics at CERN.

The point is that "strongly interacting particles" is a very clumsy term which does not yield itself to the formation of an adjective.

Massless virtual gluons compose the overwhelming majority of particles inside hadrons, as well as the major constituents of its mass (with the exception of the heavy charm and bottom quarks; the top quark vanishes before it has time to bind into a hadron).

One outcome is that short-lived pairs of virtual quarks and antiquarks are continually forming and vanishing again inside a hadron.

This means that baryons (composite particles made of three, five or a larger odd number of quarks) have B = 1 whereas mesons have B = 0.

For example, at very high temperature and high pressure, unless there are sufficiently many flavors of quarks, the theory of quantum chromodynamics (QCD) predicts that quarks and gluons will no longer be confined within hadrons, "because the strength of the strong interaction diminishes with energy".

This property, which is known as asymptotic freedom, has been experimentally confirmed in the energy range between 1 GeV (gigaelectronvolt) and 1 TeV (teraelectronvolt).

Examples of mesons commonly produced in particle physics experiments include pions and kaons.

Pions also play a role in holding atomic nuclei together via the residual strong force.