Meson

Outside of the nucleus, mesons exist as short-lived byproducts of very high energy collisions between particles made of quarks. Mesons can be produced artificially in a cyclotron, in the collision of protons, antiprotons, or other particles. 

Higher energy, more massive mesons, were created momentarily after the Big Bang. However, they are not thought to play a role in nature today. Despite this, such heavy mesons are regularly created in particle accelerators. This is to understand the nature of the heavier types of quarks that make up the heavier mesons. 

Mesons are hadrons. These are particles composed of 2 or more quarks. The other members of the hadron family are baryons, which are composed of an odd number of quarks, at least 3. There has also been experimental evidence in support of exotic mesons, which have 4 or more quarks. 

Quarks have a spin of 1/2 integer, they are fermions. Conventional 2 quark mesons are bosons, while the odd-numbered baryons are fermions. 

Each type of meson has a corresponding antiparticle or "antimeson." This is where the quarks are replace by their corresponding antiquarks and vice versa. For example, the positive pion, which is composed of 1 up quark and 1 down antiquark. It's corresponding antiparticle is the negative pion. It is made up of 1 up antiquark and 1 down quark. 

Mesons, composed of quarks, participate in both the weak and strong nuclear interactions. Mesons that carry a net electric charge also participate in the electromagnetic interaction.