A meson is a subatomic particle that consists of one quark and one antiquark, bound together by a formidable force. The strong force is the strongest of all four forces, and it is responsible for holding protons and neutrons together in atoms and binding quarks together to form hadrons like mesons. Mesons are produced in high-energy collisions between particles, such as in cosmic ray interactions or during collisions at particle accelerators.
[See Anderson and Neddermeyer, Physical Review, vol. 54, p. 88 (1938)]
Mesons are classified according to their spin, which can be either an integer or a half-integer. Integer spin mesons are called bosons, while half-integer spin mesons are called fermions. Bosonic meson states include the π (pion), K (kaon), and (eta) η particles, while fermionic meson states include the D0, B0, and J/psi particles. The most crucial difference between these two types of mesons is that bosonic mesons can exist in either a ground state or an excited state. In contrast, due to the Pauli exclusion principle, fermionic mesons must always be found in an excited state.
The lifetime of a meson varies depending on its type but ranges from 10-6 to 10−24 seconds. Some notable exceptions, however, are the π+and K+ which have lifetimes of 2×10−8 seconds and 5×10−8 seconds, respectively, due to their decays into mu +νμ (muon plus antineutrino). Other decay modes include decay into photons or leptoquarks.