Quark.docx

Quark.docx

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Quark

Quark

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Thisarticleisabouttheparticle.Forotheruses,seeQuark（disambiguation）.

Quark

Aproton,composedoftwoupquarksandonedownquark.（Thecolorassignmentofindividualquarksisnotimportant,onlythatallthreecolorsarepresent.）

Composition

Elementaryparticle

Statistics

Fermionic

Generation

1st,2nd,3rd

Interactions

Electromagnetism,Gravitation,Strong,Weak

Symbol

q

Antiparticle

Antiquark（q）

Theorized

MurrayGell-Mann（1964）

GeorgeZweig（1964）

Discovered

SLAC（~1968）

Types

6（up,down,strange,charm,bottom,andtop）

Electriccharge

+2⁄3 e,−1⁄3 e

Colorcharge

Yes

Spin

1⁄2

Baryonnumber

1⁄3

Aquark（ /ˈkwɔrk/or/ˈkwɑrk/）isanelementaryparticleandafundamentalconstituentofmatter.Quarkscombinetoformcompositeparticlescalledhadrons,themoststableofwhichareprotonsandneutrons,thecomponentsofatomicnuclei.[1]Duetoaphenomenonknownascolorconfinement,quarksareneverdirectlyobservedorfoundinisolation;theycanonlybefoundwithinbaryonsormesons.[2][3]Forthisreason,muchofwhatisknownaboutquarkshasbeendrawnfromobservationsofthehadronsthemselves.

Therearesixtypesofquarks,knownasflavors:

up,down,strange,charm,bottom,andtop.[4]Upanddownquarkshavethelowestmassesofallquarks.Theheavierquarksrapidlychangeintoupanddownquarksthroughaprocessofparticledecay:

thetransformationfromahighermassstatetoalowermassstate.Becauseofthis,upanddownquarksaregenerallystableandthemostcommonintheuniverse,whereasstrange,charm,top,andbottomquarkscanonlybeproducedinhighenergycollisions（suchasthoseinvolvingcosmicraysandinparticleaccelerators）.

Quarkshavevariousintrinsicproperties,includingelectriccharge,colorcharge,spin,andmass.QuarksaretheonlyelementaryparticlesintheStandardModelofparticlephysicstoexperienceallfourfundamentalinteractions,alsoknownasfundamentalforces（electromagnetism,gravitation,stronginteraction,andweakinteraction）,aswellastheonlyknownparticleswhoseelectricchargesarenotintegermultiplesoftheelementarycharge.Foreveryquarkflavorthereisacorrespondingtypeofantiparticle,knownasantiquark,thatdiffersfromthequarkonlyinthatsomeofitspropertieshaveequalmagnitudebutoppositesign.

ThequarkmodelwasindependentlyproposedbyphysicistsMurrayGell-MannandGeorgeZweigin1964.[5]Quarkswereintroducedaspartsofanorderingschemeforhadrons,andtherewaslittleevidencefortheirphysicalexistenceuntildeepinelasticscatteringexperimentsattheStanfordLinearAcceleratorCenterin1968.[6][7]Allsixflavorsofquarkhavesincebeenobservedinacceleratorexperiments;thetopquark,firstobservedatFermilabin1995,wasthelasttobediscovered.[5]

Contents

 [hide] 

∙1Classification

∙2History

∙3Etymology

∙4Properties

o4.1Electriccharge

o4.2Spin

o4.3Weakinteraction

o4.4Stronginteractionandcolorcharge

o4.5Mass

o4.6Tableofproperties

∙5Interactingquarks

o5.1Seaquarks

o5.2Otherphasesofquarkmatter

∙6Seealso

∙7Notes

∙8References

∙9Furtherreading

∙10Externallinks

[edit]Classification

Seealso:

StandardModel

SixoftheparticlesintheStandardModelarequarks（showninpurple）.Eachofthefirstthreecolumnsformsagenerationofmatter.

TheStandardModelisthetheoreticalframeworkdescribingallthecurrentlyknownelementaryparticles,aswellastheunobserved[nb1]Higgsboson.[8]Thismodelcontainssixflavorsofquarks（q）,namedup（u）,down（d）,strange（s）,charm（c）,bottom（b）,andtop（t）.[4]Antiparticlesofquarksarecalledantiquarks,andaredenotedbyabaroverthesymbolforthecorrespondingquark,suchasuforanupantiquark.Aswithantimatteringeneral,antiquarkshavethesamemass,meanlifetime,andspinastheirrespectivequarks,buttheelectricchargeandotherchargeshavetheoppositesign.[9]

Quarksarespin-1⁄2particles,implyingthattheyarefermionsaccordingtothespin-statisticstheorem.TheyaresubjecttothePauliexclusionprinciple,whichstatesthatnotwoidenticalfermionscansimultaneouslyoccupythesamequantumstate.Thisisincontrasttobosons（particleswithintegerspin）,anynumberofwhichcanbeinthesamestate.[10]Unlikeleptons,quarkspossesscolorcharge,whichcausesthemtoengageinthestronginteraction.Theresultingattractionbetweendifferentquarkscausestheformationofcompositeparticlesknownashadrons（see"Stronginteractionandcolorcharge"below）.

Thequarkswhichdeterminethequantumnumbersofhadronsarecalledvalencequarks;apartfromthese,anyhadronmaycontainanindefinitenumberofvirtual（orsea）quarks,antiquarks,andgluonswhichdonotinfluence