Hadron - Wikipedia, The Free Encyclopedia

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Hadron From Wikipedia, the free encyclopedia In particle physics, a hadron i /ˈhædrɒn/ (Greek: ἁδρός, hadrós, stout, thick ) is a composite particle made of quarks held together by the strong force (in the same way as atoms and molecules are held together by the electromagnetic force). Hadrons are categorized into two families: baryons (such as protons and neutrons, made of three quarks) and mesons (such as pions, made of one quark and one antiquark). Other types of hadron may exist, such as t
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  Alltypes of hadronshavezero total color charge.(threeexamples shown) Hadron From Wikipedia, the free encyclopedia In particle physics, a hadron i  /  ˈ hædr  ɒ n/ (Greek: ἁδρός , hadrós , stout, thick ) is a composite particle made of quarks held together bythe strong force (in the same way as atoms andmolecules are held together bythe electromagnetic force).Hadrons are categorized into two families: baryons (such as protons and neutrons, made of three quarks) and mesons (such as pions, made of one quark and one antiquark). Other types of hadron may exist, such as tetraquarks (or, more generally, exotic mesons) and pentaquarks (exotic baryons), but no current evidence conclusively suggests their existence. [1][2] Of the hadrons, protons and neutrons bound to atomic nuclei are stable, while others are unstable under ordinary conditions; free neutrons decay in 15 minutes. Experimentally, hadronphysics is studied bycolliding protons or nuclei of heavy elements such as lead, and detecting the debris in the produced particle showers. Contents 1 Etymology2 Properties3 Baryons4 Mesons5 See also6 References Etymology The term hadron was introduced byLev B. Okun in a plenarytalk at the 1962 InternationalConference on High Energy Physics. [3] In this talk he said:Not withstanding the fact that this report deals with weak interactions, we shall frequently have to speak of stronglyinteracting particles. These particles pose not onlynumerous scientific problems, but also a terminological problem. The point is that stronglyinteracting particles is a very clumsy term which does not yield itself to theformation of an adjective. For this reason, to take but one instance, decays into stronglyinteracting particles are called non-leptonic. This definition is not exact because non-leptonic may also signify photonic . In this report I shall call stronglyinteracting particles hadrons , and the corresponding decays hadronic (the Greek  ἁδρός  signifies large , massive , in contrast to λεπτός  which means small , light ). I hope that this terminology will prove to be convenient. –Lev B. Okun, 1962 Properties According to the quark model, [4] the properties of hadrons are primarilydetermined by their so-called valence quarks . For example, a proton is composedof two up quarks (each with electric charge + 2  ⁄  3 , for a total of + 4  ⁄  3 together) and one down quark (with electric charge − 1  ⁄  3 ). Adding these together yieldsthe proton charge of +1. Although quarks also carrycolor charge, hadrons must have zero total color charge because of a phenomenon called colorconfinement. That is, hadrons must be colorless or white . These are the simplest of the two ways: three quarks of different colors, or a quark of onecolor and an antiquark carrying the corresponding anticolor. Hadrons with the first arrangement are called baryons, and those with the second arrangementare mesons.Like all subatomic particles, hadrons are assigned quantum numbers corresponding to the representations of the Poincaré group: J  PC  ( m ), where J  is thespin quantum number, P the intrinsic parity (or P-parity), and C  , the charge conjugation (or C-parity), and the particle's mass, m . Note that the mass of ahadron 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 interaction. Hadrons may also carryflavor quantum numbers such as isospin (or G parity), and strangeness. All quarkscarryan additive, conserved quantum number called a baryon number (  B ), which is + 1  ⁄  3 for quarks and − 1  ⁄  3 for antiquarks. This means that baryons(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; several hundreds of resonances have beenobserved in particle physics experiments. Resonances decay extremely quickly (within about 10 −24 seconds) via the strong nuclear force.In other phases of matter the hadrons may disappear. For example, at very high temperature and high pressure, unless there are sufficiently many flavors of quarks, the theoryof quantum chromodynamics (QCD) predicts that quarks and gluons willno longer be confined within hadrons because the strength of the strong interaction diminishes with energy . This property, which is known as asymptotic freedom, has been experimentally confirmed in the energyrange between 1 GeV (gigaelectronvolt) and 1 TeV (teraelectronvolt). [5] All free hadrons except the proton (and antiproton) are unstable. Baryons  Main article: Baryon All known baryons are made of three valence quarks, so they are fermions (i.e., they have odd half-integral spin because they have an odd number of quarks). As quarks possess baryon number B = 1  ⁄  3 , baryons have baryon number B = 1. The best-known baryons are the proton and the neutron.One can hypothesise baryons with further quark–antiquark pairs in addition to their three quarks. Hypothetical baryons with one extra quark–antiquark pair (5 quarks in all) are calledpentaquarks. [6] Several pentaquark candidates were found in the early2000s, but upon further review these states have now been established as non-existent. [7] (This does not rule againstpentaquarks in general, only the candidates put forward).Each type of baryon has a corresponding antiparticle (antibaryon) in which quarks are replaced bytheir corresponding antiquarks. For example, just as a proton is made of two up-quarksand one down-quark, its corresponding antiparticle, the antiproton, is made of two up-antiquarks and one down-antiquark. Mesons  Main article: Meson Mesons are hadrons composed of a quark–antiquark pair. Theyare bosons (integral spin—i.e., 0, 1, or -1—as they have an even number of quarks). Theyhave baryon number B = 0.Examples of mesons commonly produced in particle physics experiments include pions and kaons. Pions also play a role in holding atomic nuclei together via the residual strong force.In principle, mesons with more than one quark–antiquark pair may exist; a hypothetical meson with two pairs is called a tetraquark. Several tetraquark candidates were found in the 2000s,but their status is under debate [8] . Several other hypothetical exotic mesons lie outside the quark model of classification. These include glueballs and hybrid mesons (mesons bound byexcited gluons).  See also Hadronization, the formation of hadrons out of quarks and gluonsLarge Hadron Collider (LHC)List of particlesStandard modelSubatomic particlesHadron therapy, aka Particle beam therapy References 1. ^ W.-M.Yao et al. (2006): Particlelistings – Θ + (http://pdg.lbl.gov/2006/reviews/theta_b152.pdf)2. ^ C.Amsler et al. (2008): Pentaquarks (http://pdg.lbl.gov/2008/reviews/pentaquarks_b801.pdf)3. ^ LevB.Okun (1962). The Theoryof WeakInteraction . Proceedings of 1962 International Conference on High-Energy Physics at CERN  .Geneva.p. 845.Bibcode:1962hep..conf..845O(http:// adsabs.harvard.edu/abs/1962hep..conf..845O).4. ^ C.Amsler et al. (ParticleDataGroup) (2008). Reviewof ParticlePhysics – Quark Model (http://pdg.lbl.gov/2008/reviews/quarkmodrpp.pdf). Physics Letters B 667 : 1.Bibcode:2008PhLB..667....1P (http:// adsabs.harvard.edu/abs/2008PhLB..667....1P).doi:10.1016/j.physletb.2008.07.018 (http://dx.doi.org/10.1016%2Fj.physletb.2008.07.018).5. ^ S.Bethke(2007). Experimentaltests of asymptotic freedom . Progressin Particle andNuclearPhysics 58 (2): 351.arXiv:hep-ex/0606035 (http://arxiv.org/abs/hep-ex/0606035).Bibcode:2007PrPNP..58..351B(http://adsabs.harvard.edu/abs/2007PrPNP..58..351B).doi:10.1016/j.ppnp.2006.06.001 (http://dx.doi.org/10.1016%2Fj.ppnp.2006.06.001).6. ^ S.Kabana (2005). AIPConferenceProceedings .arXiv:hep-ex/0503020 (http://arxiv.org/abs/hep-ex/0503020) [hep-ex (http://arxiv.org/archive/hep-ex)].doi:10.1063/1.1920947 (http:// dx.doi.org/10.1063%2F1.1920947).7. ^ C.Amsler et al. (ParticleDataGroup) (2008). Reviewof ParticlePhysics – Pentaquarks (http://pdg.lbl.gov/2008/reviews/pentaquarks_b801.pdf). Physics Letters B 667 : 1.Bibcode:2008PhLB..667....1P(http://adsabs.harvard.edu/abs/2008PhLB..667....1P).doi:10.1016/j.physletb.2008.07.018(http://dx.doi.org/10.1016%2Fj.physletb.2008.07.018).8. ^ http://www.wired.com/wiredscience/2013/06/four-quark-particle/  Retrieved from http://en.wikipedia.org/w/index.php?title=Hadron&oldid=561494838 Categories: Hadrons Particle physics Nuclear physicsThis page was last modified on 25 June 2013 at 10:25.Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. By using this site, you agree to the Terms of Use and PrivacyPolicy.Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization.
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