Dictionary:
had·ron (hăd'rŏn') ![]() |
Any of a class of subatomic particles that are composed of quarks and take part in the strong interaction.
[Greek hadros, thick + –ON1.]
hadronic had·ron'ic adj.
Dictionary:
had·ron (hăd'rŏn') ![]() |
Any of a class of subatomic particles that are composed of quarks and take part in the strong interaction.
[Greek hadros, thick + –ON1.]
hadronic had·ron'ic adj.| 5min Related Video: hadron |
| Sci-Tech Encyclopedia: Hadron |
The generic name of a class of particles which interact strongly with one another. Examples of hadrons are protons, neutrons, the π, K, and D mesons, and their antiparticles. Protons and neutrons, which are the constituents of ordinary nuclei, are members of a hadronic subclass called baryons, as are strange and charmed baryons. Baryons have half-integral spin, obey Fermi-Dirac statistics, and are known as fermions. Mesons, the other subclass of hadrons, have zero or integral spin, obey Bose-Einstein statistics, and are known as bosons. The electric charges of baryons and mesons are either zero or ±1 times the charge on the electron. Masses of the known mesons and baryons cover a wide range, extending from the pi meson, with a mass approximately one-seventh that of the proton, to values of the order of 10times the proton mass. The spectrum of meson and baryon masses is not understood. See also Baryon;
Based on an enormous body of data, hadrons are now thought of as consisting of elementary fermion constituents known as quarks which have electric charges of +
|e| and
|e|, where |e| is the absolute value of the electron charge. For example, a quark-antiquark pair makes up a meson, while three quarks constitute a baryon. See also
| Britannica Concise Encyclopedia: hadron |
For more information on hadron, visit Britannica.com.
| WordNet: hadron |
The noun has one meaning:
Meaning #1:
any elementary particle that interacts strongly with other particles
| Wikipedia: Hadron |
In particle physics, hadron (pronounced /ˈhædrɒn/, from the Greek: ἁδρός, hadrós, "stout, thick") is one of the two groups of particles (the other being lepton). Hadron is the group containing all particles that interact with the strong force. Hadrons are held together by the strong force, similarly to how molecules are held together by the electromagnetic force. All hadrons are made up of quarks. There are two subsets of hadrons: baryons and mesons; the most well known baryons are protons and neutrons.
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According to the quark model,[1] the properties of hadrons are primarily determined by their so-called valence quarks. For example, a proton is composed of two up quarks (each with electric charge +2/3) and one down quark (with electric charge -1/3). Adding these together yields the proton charge of +1. Although the constituent quarks also carry color charge (nothing to do with visual color), a property of the strong nuclear force called color confinement requires that any composite state carry no residual color charge. That is, hadrons must be colorless. There are two ways to accomplish this: three quarks of different colors, or a quark of one color and an anti-quark carrying the corresponding anticolor. Hadrons based on the former are called baryons, and those based on the latter are called mesons.
Like all subatomic particles, hadrons are assigned quantum numbers corresponding to the representations of the Poincaré group: JPC(m), where J is the spin quantum number, P, the intrinsic (or P) parity, and C, the charge conjugation, or C parity, and the particle four-momentum, m, (i.e., its mass). Note that the mass of a hadron has very little to do with the mass of its valence quarks; rather, due to mass–energy equivalence, most of the mass comes from the large amount of energy associated with the strong nuclear force. Hadrons may also carry flavor quantum numbers such as isospin (or G parity), and strangeness. All quarks carry an additive, conserved quantum number called a baryon number (B), which is +1/3 for quarks and -1/3 for antiquarks. This means that baryons—which are groups of three quarks—have B=1 while mesons have B=0.
Hadrons have excited states known as resonances. Each ground-state hadron may have several excited states; hundreds of resonances have been observed in particle physics experiments. Resonances decay extremely quickly (within about 10−24 seconds) via the strong nuclear force.
In other phases of QCD matter the hadrons may disappear. For example, at very high temperature and high pressure, unless there are sufficiently many flavors of quarks, the theory of quantum chromodynamics (QCD) predicts that quarks and gluons will interact weakly and will no longer be confined within hadrons. This property, which is known as asymptotic freedom, has been experimentally confirmed at the energy scales between a GeV and a TeV.[2]
All free hadrons except the proton are unstable.
All known baryons are made of three valence quarks, and are therefore fermions. They have baryon number B=1, while antibaryons (composed of three antiquarks) have B=-1. In principle, some baryons could be composed of further quark-antiquark pairs in addition to the three quarks (or antiquarks) that make up basic baryons. Baryons containing a single additional quark-antiquark pair are called pentaquarks.[3] Evidence for these states was claimed by several experiments in the early 2000s, though this has since been refuted[4]. No evidence of baryon states with even more quark-antiquark pairs has been found.
Mesons are bosons composed of a quark-antiquark pair. They have baryon number B=0. Examples of mesons commonly produced in particle physics experiments include pions and kaons. The former also play a role holding atomic nuclei together via the residual strong force. Hypothetical mesons have more than one quark-antiquark pair; a meson composed of two of these pairs is called a tetraquark. Currently there is no evidence of their existence. Mesons that lie outside the quark model classification are called exotic mesons. These include glueballs and hybrid mesons (mesons bound by excited gluons).
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| bare charm (particle physics) | |
| glueball (particle physics) | |
| strange particle (particle physics) |
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![]() | Dictionary. The American Heritage® Dictionary of the English Language, Fourth Edition Copyright © 2007, 2000 by Houghton Mifflin Company. Updated in 2007. Published by Houghton Mifflin Company. All rights reserved. Read more | |
![]() | Sci-Tech Encyclopedia. McGraw-Hill Encyclopedia of Science and Technology. Copyright © 2005 by The McGraw-Hill Companies, Inc. All rights reserved. Read more | |
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![]() | Wikipedia. This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Hadron". Read more |
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