| Particle physics, also called
"high energy physics," is the study of the fundamental particles and their
interactions. To explore such particles at the requisite
subatomic distance scales requires particles with high energies.
Most experiments use particle accelerators to provide such particles, but
it is also possible to use cosmic rays, a small fraction of which have
energies well beyond the reach of accelerators.
According to our present understanding, which is embodied in a model known as the Standard Model, the true elementary particles - the building blocks of matter as we know it - are quarks and leptons. They interact through three types of interactions - Strong, Electromagnetic, and Weak (although we know the gravitational interaction exists, it hasn't been incorporated effectively into the model yet). Quarks interact strongly and are thought to be the constituents of all strongly interacting observed particles, which are called hadrons. Neutrons, protons, mesons and hyperons are some of the more familiar hadrons. The Strong force holds the quarks together so strongly inside of hadrons that they are unable to exist as free particles. Leptons are not susceptible to the strong force (we say they have a “strong charge” of zero), and can therefore be observed as free particles. Leptons include electrons, muons, tau's, with an associated neutrino for each of these. |