Leptons, mesons, and pi-mesons (or pions) are all types of subatomic particles.
Leptons: Leptons are a class of elementary particles that do not participate in the strong nuclear force. They are considered fundamental particles, meaning they are not composed of smaller particles. Leptons have a half-integer spin and are not affected by the strong interaction, but they do experience the weak nuclear force and electromagnetic force. Examples of leptons include electrons, muons, and neutrinos, along with their corresponding antiparticles.
Mesons: Mesons are composite particles made up of a quark and an antiquark bound together by the strong nuclear force. They belong to the category of hadrons, which includes both mesons and baryons. Mesons have an integer spin and are affected by the strong interaction. They are unstable and have relatively short lifetimes. Examples of mesons include pions, kaons, and the J/psi meson.
Pi-mesons (Pions): Pions, often referred to as pi-mesons, are a specific type of meson. They are the lightest mesons and have a spin of zero. Pions are composed of either an up quark and an anti-down quark (π+) or a down quark and an anti-up quark (π-). Pions are involved in mediating the strong nuclear force between nucleons (protons and neutrons) within atomic nuclei. They also play a role in nuclear reactions and interactions.
It's worth noting that pions are often referred to as mesons, but not all mesons are pions. Mesons can consist of various combinations of quarks and antiquarks, while pions specifically refer to the π+ and π- particles.