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A muon is a subatomic particle with a negative charge that is similar to an electron in that it has a negative charge and a similar spin. For simplicity, they are commonly represented by the Greek letter mu, or μ. Muons are considered elementary particles. Elementary particles are subatomic particles that are not known to have substructures. While an atom is made up of protons, neutrons, electrons, and other particles, elementary particles are not known to be made up of any smaller particles.
The primary difference between a muon and an electron is mass. Muons contain about 200 times more mass than electrons. Essentially, they are much heavier versions of electrons. Consequently, they are much more penetrating than the lighter electrons are.
Along with the electron, the tauon, and the three neutrinos, the muon is considered a lepton. Leptons are one of the families of elementary particles that are considered the building blocks of matter. The quark is another elementary particle that receives this classification; leptons and quarks are widely considered to be the most basic building blocks of matter.
While studying cosmic radiation in 1936, Carl D. Anderson, an American physicist, discovered the muon. He noticed that the particles curved at a different angle than other known subatomic particles when passed through a magnetic field, and determined that this was because of a difference in mass. The discovery of the muon shocked the scientific community because its existence was completely unexpected and unpredicted. Soon after, several other different subatomic particles with different masses were discovered, and the term muon was coined to distinguish Anderson's discovery from the rest.
Muons only form very high-energy events and situations. Neither normal radioactive decay nor nuclear fusion, such as occurs in nuclear reactors and nuclear bombs, are energetic enough to produce muons. Most muons that reach the earth come from distant cosmic rays from space. When cosmic ray protons collide with the nuclei of Earth's air particles, muons are produced.
All elementary particles have corresponding antiparticles of opposite charge. They do, however, have the same charge and spin. The antiparticle of a muon is the positively-charged antimuon. The antimuon is sometimes simply called the positive muon, as it has a positive charge.