Find the word definition

Crossword clues for meson

The Collaborative International Dictionary

Meson \Mes"on\, n. [NL., fr. Gr. me`son middle, neut. of me`sos, a., middle.]

  1. (Anat.) The mesial plane dividing the body of an animal into similar right and left halves. The line in which it meets the dorsal surface has been called the dorsimeson, and the corresponding ventral edge the ventrimeson.
    --B. G. Wilder.

  2. (Physics) An elementary particle made up of two quarks; a hadron having a baryon number of zero; any hadron other than a baryon. Mesons are bosons with integral values of spin, having a mass intermediate between those of the electron and a nucleon; they may have positive or negative charges, or may be neutral. Mesons are of three types: the pion ([pi]-meson), kaon (K-mesons), and [eta]-mesons.

    mu meson (Physics) the former name for the muon, a particle which is not a true meson[2]. The term is no longer used in technical literature, except historically.

Douglas Harper's Etymology Dictionary

subatomic particle, 1939, from Greek mesos "middle" (see medial (adj.)) + subatomic particle suffix -on. Earlier mesotron (1938). So called for being intermediate in mass between protons and electrons.


Etymology 1 n. (context rare outside entomology English) The mesial plane dividing the body into similar right and left halves. Etymology 2

n. 1 (context obsolete English) A member of a group of subatomic particles having a mass intermediate between electrons and protons. (The most easily detected mesons fit this definition.) 2 (context now specifically particle English) An elementary particle that is composed of a quark and an antiquark, such as a kaon or pion. (Mesons composed of rarer quarks are much heavier.)


n. an elementary particle responsible for the forces in the atomic nucleus; a hadron with a baryon number of 0 [syn: mesotron]


In particle physics, mesons ( or ) are hadronic subatomic particles composed of one quark and one antiquark, bound together by the strong interaction. Because mesons are composed of sub-particles, they have a physical size, with a diameter of roughly one fermi, which is about the size of a proton or neutron. All mesons are unstable, with the longest-lived lasting for only a few hundredths of a microsecond. Charged mesons decay (sometimes through intermediate particles) to form electrons and neutrinos. Uncharged mesons may decay to photons. Both of these decays imply that color is no longer a property of the by products.

Mesons are not produced by radioactive decay, but appear in nature only as short-lived products of very high-energy interactions in matter, between particles made of quarks. In cosmic ray interactions, for example, such particles are ordinary protons and neutrons. Mesons are also frequently produced artificially in high-energy particle accelerators that collide protons, anti-protons, or other particles.

In nature, the importance of lighter mesons is that they are the associated quantum-field particles that transmit the nuclear force, in the same way that photons are the particles that transmit the electromagnetic force. The higher energy (more massive) mesons were created momentarily in the Big Bang, but are not thought to play a role in nature today. However, such particles are regularly created in experiments, in order to understand the nature of the heavier types of quark that compose the heavier mesons.

Mesons are part of the hadron particle family, and are defined simply as particles composed of two quarks. The other members of the hadron family are the baryons: subatomic particles composed of three quarks rather than two. Some experiments show evidence of exotic mesons, which do not have the conventional valence quark content of one quark and one antiquark.

Because quarks have a spin of , the difference in quark-number between mesons and baryons results in conventional two-quark mesons being bosons, whereas baryons are fermions.

Each type of meson has a corresponding antiparticle (antimeson) in which quarks are replaced by their corresponding antiquarks and vice versa. For example, a positive pion is made of one up quark and one down antiquark; and its corresponding antiparticle, the negative pion , is made of one up antiquark and one down quark.

Because mesons are composed of quarks, they participate in both the weak and strong interactions. Mesons with net electric charge also participate in the electromagnetic interaction. They are classified according to their quark content, total angular momentum, parity and various other properties, such as C-parity and G-parity. Although no meson is stable, those of lower mass are nonetheless more stable than the most massive mesons, and are easier to observe and study in particle accelerators or in cosmic ray experiments. They are also typically less massive than baryons, meaning that they are more easily produced in experiments, and thus exhibit certain higher energy phenomena more readily than baryons composed of the same quarks would. For example, the charm quark was first seen in the J/Psi meson in 1974, and the bottom quark in the upsilon meson in 1977.

Usage examples of "meson".

When the stylus fired a coherent beam of mesons at the border, the razor wire of disrupted graphs sliced fragments of their own surreal dimensions from the knot of virtual quarks and gluons making up each meson, and it was possible to exploit coherence effects to make some of these fragments act in unison to modify the border itself.

And when a proton annihilates an antiproton, it produces a pi-zero meson one-third of the time, and a charged pion, a muon, and a neutrino two-thirds of the time, after which the pions and neutrons promptly break down to electrons and positrons, photons and neutrinos.

Nuclear particles, known as mu mesons or muons, are continually falling onto the surface of Earth.

Bright drops dissolved in moving toward the hollow sphere, merged with other drops as the shimmering spiral began an ancient lay of galaxies and mesons and the hearts of neutron stars.

Did they really believe quarks and mesons inspired the average human being?

He went on to inform his antagonist that even now tractor beams were hauling stuff into one of the insulated holds, raw hot stuff at a few thousand degrees, mesons, protons, corpuscles, wave particlesa great trail of material smaller than dust, all of which the Beatitude would use for fuel or building material.

The whole kit-and-caboodle of pions, mesons, gluinos, antineutrinos, that whole strange charm of quarkiness, may come to seem a very twentieth-century enthusiasm.

Conceptually, the universe had been a reasonably comfortable place to live in, in primitive atomic theory which offered the assurance that everything, earth, air, fire or water, steel and oranges, man or star, was ultimately composed of submicroscopic vortices called protons and electrons leavened a little with neutrons and neutrinos which had no charge, and bound together by a disorderly but homely family of mesons.

They were watching (via some very indirect instruments) the decay of a lambda particle into a proton plus a pi meson.

The separation of color would be minute, but the effects would be dramatic: the two orbiting, polarized cores would generate powerful jets of mesons, which would act to brake the neutron stars' orbital motion a kind of nuclear analogue of gravitational radiation, but mediated by the strong force and hence much more energetic.

Music is first and foremost a function of the particular instrument, the reed pipe, the skin drum, the human throat—it is a function of tangibles which a race operating upon elec­trons, positrons and mesons would never encounter in the course of its construc­tion.