muon

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muon

(myo͞o`ŏn), elementary particleelementary particles,
the most basic physical constituents of the universe. Basic Constituents of Matter

Molecules are built up from the atom, which is the basic unit of any chemical element. The atom in turn is made from the proton, neutron, and electron.
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 heavier than an electronelectron,
elementary particle carrying a unit charge of negative electricity. Ordinary electric current is the flow of electrons through a wire conductor (see electricity). The electron is one of the basic constituents of matter.
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 but lighter than other particles having nonzero rest mass. The name muon is derived from mu meson, the former name of the particle. The muon was first observed in cosmic rayscosmic rays,
charged particles moving at nearly the speed of light reaching the earth from outer space. Primary cosmic rays consist mostly of protons (nuclei of hydrogen atoms), some alpha particles (helium nuclei), and lesser amounts of nuclei of carbon, nitrogen, oxygen, and
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 by Carl D. Anderson and Seth Neddermeyer in 1936, the year after the existence of a particle of about the same mass had been predicted by Hideki Yukawa. However, the muon's behavior did not conform to that of Yukawa's mesonmeson
[Gr.,=middle (i.e., middleweight)], class of elementary particles whose masses are generally between those of the lepton class of lighter particles and those of the baryon class of heavier particles. From a technical point of view mesons are strongly interacting bosons; i.
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 theory (which actually describes the pionpion
or pi meson,
lightest of the meson family of elementary particles. The existence of the pion was predicted in 1935 by Hideki Yukawa, who theorized that it was responsible for the force of the strong interactions holding the atomic nucleus together.
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, discovered more than 10 years later), and the muon is now classed as a leptonlepton
[Gr.,=light (i.e., lightweight)], class of elementary particles that includes the electron and its antiparticle, the muon and its antiparticle, the tau and its antiparticle, and the neutrino and antineutrino associated with each of these particles.
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 rather than a meson. The muon resembles the electron in every way except mass, the muon having 207 times the mass of the electron. Each particle is negatively charged and has a positively charged antiparticleantiparticle,
elementary particle corresponding to an ordinary particle such as the proton, neutron, or electron, but having the opposite electrical charge and magnetic moment.
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; each has half-integer spin and participates in the weak nuclear forceforce,
commonly, a "push" or "pull," more properly defined in physics as a quantity that changes the motion, size, or shape of a body. Force is a vector quantity, having both magnitude and direction.
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 but not in the strong force; and each has an associated neutrinoneutrino
[Ital.,=little neutral (particle)], elementary particle with no electric charge and a very small mass emitted during the decay of certain other particles. The neutrino was first postulated in 1930 by Wolfgang Pauli in order to maintain the law of conservation of energy
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 and antineutrino. Muons are produced by the weak decay of pions into a muon and a muon antineutrino. The muon differs from the electron in that it is unstable, decaying with an average lifetime of 2.2 × 10−6 sec (2.2 microseconds) into an electron or positron and a pair of neutrinos, but this difference is related to the difference in mass; the electron is stable because there is no lighter particle into which it can decay. Muons can be substituted for electrons in orbit around the nucleus of an atom; the resulting atom is long-lived enough to exhibit behavior that further supports the close resemblance between the muon and the electron. Recent studies of muons have included the production of "muonic atoms" (ordinary atoms to which an orbiting muon is added) and muonium, which consists of an electron in orbit around a positive muon.

muon

(myoo -on) Symbol: μ. An elementary particle (a lepton) with the same charge and spin as an electron but with a mass that is 207 times greater. It decays into electrons and neutrinos with a lifetime of two microseconds. Cosmic-ray showers detected on Earth are comprised mainly of muons produced by pion decay. Muons do not interact strongly with matter and hence a large proportion of them reach the Earth's surface. The antiparticle of the muon is the antimuon.

muon

[′myü‚än]
(particle physics)
Collective name for two semistable elementary particles with positive and negative charge, designated μ+and μ- respectively, which are leptons and have a spin of ½ and a mass of approximately 105.7 MeV. Also known as mu meson.

muon

a positive or negative elementary particle with a mass 207 times that of an electron and spin ½. It was originally called the mu meson but is now classified as a lepton
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