AskDefine | Define hadron

Dictionary Definition

hadron n : any elementary particle that interacts strongly with other particles

User Contributed Dictionary



  1. A strongly interacting particle such as a proton. A particle which is affected by the strong nuclear force. A hadron is composed of quarks.


Extensive Definition

A hadron (, from Greek , hadros, thick), in particle physics, is any strongly interacting composite subatomic particle. All hadrons are composed of quarks. Hadrons are divided into two classes:
  • Baryons, strongly interacting fermions such as a neutron or a proton, made up of three quarks.
  • Mesons, strongly interacting bosons consisting of a quark and an antiquark.
Notice that mesons are composite bosons, but they are not composed of bosons (quarks are fermions).
Like all subatomic particles, hadrons have quantum numbers corresponding to the representations of the Poincaré group: JPC(m), where J is the spin, P, the parity, C, the C parity, and m, the mass. In addition they may carry flavour quantum numbers such as isospin (or G parity), strangeness etc. Moreover,
Most hadrons can be classified by the quark model which posits that all the quantum numbers are derived from those of the valence quarks (the quarks which form the hadron). For instance, since each quark has B=1/3, each baryon, composed of three quarks, has B=1.
Excited baryon or meson states are known as resonances. Each ground state hadron may have many excited states, and hundreds have been observed in particle experiments. Resonances decay extremely quickly (within about 10−24 s) via strong interactions.
Mesons which lie outside the quark model classification are called exotic mesons. These include glueballs, hybrid mesons and tetraquarks. The only baryons which lie outside the quark model at present are the pentaquarks, but evidence for their existence is unclear as of 2006.
All hadrons are single particle excitations of the basic theory of strong interactions, called quantum chromodynamics. Due to a property called confinement that this theory enjoys at energies below the QCD scale, these excitations are not quarks and gluons, which are the basic fields, but the hadrons which are composite, and carry no color charge.
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, QCD predicts that quarks and gluons will interact weakly and in particular no longer be confined. This property, which is known as asymptotic freedom, has been experimentally confirmed at the energy scales between a GeV and a TeV.

References and external links

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hadron in Bengali: হ্যাড্রন
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hadron in Bulgarian: Адрон
hadron in Catalan: Hadró
hadron in Chuvash: Адрон
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hadron in German: Hadron
hadron in Modern Greek (1453-): Αδρόνιο
hadron in Spanish: Hadrón
hadron in Persian: هادرون
hadron in French: Hadron
hadron in Croatian: Hadroni
hadron in Icelandic: Sterkeind
hadron in Italian: Adrone
hadron in Hebrew: האדרון
hadron in Latvian: Hadroni
hadron in Lithuanian: Hadronas
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hadron in Japanese: ハドロン
hadron in Norwegian: Hadron
hadron in Low German: Hadron
hadron in Polish: Hadron
hadron in Portuguese: Hádron
hadron in Russian: Адрон
hadron in Slovak: Hadrón
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hadron in Finnish: Hadroni
hadron in Swedish: Hadron
hadron in Vietnamese: Hadron
hadron in Turkish: Hadron
hadron in Ukrainian: Адрон
hadron in Urdu: ثقیلہ
hadron in Chinese: 强子
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