Composite Particles
What Happens When Elementary Particles Get Together
Beyond the elementary fermions, leptons, and bosons, are the composite particles which are made up of these elementary particles.
Baryons are a class of particles that are usually composed of three quarks, or three antiquarks. Nucleons are a special type of baryon that have three first generation quarks, either the proton (uud) or the neutron (udd). Sometimes, one of the down quarks in the neutron will decay into an up quark, and a neutron will be transmuted into a proton.
Hyperons are baryons that have at least one strange quark, but since the strange quark is so massive, hyperons do not exist for long. Baryons containing charm and bottom quarks have also been observed, but being so massive, they succumb to the same fate as hyperons. Pentaquarks are an exotic and unconfirmed class of composite particle that contain four quarks and one antiquark.
Finally mesons are a class of composite particles usually consisting of one quark and one antiquark. Like some bosons, some mesons help mediate the strong force. Mesons don't generally exist for a very long time at all, and decay into other more stable particle combinations. If the meson is composed of a quark and its antiquark, for instance and up quark and an antiup antiquark, the antiparticle of the meson is itself.
Other exotic mesons have been predicted by the Standard Model, but have not been confirmed. These include tetraquarks made of two quarks and two antiquarks, glueballs composed of multiple gluons, and hybrids composed of both quarks and gluons.
