Editing Quark (section)

{{Short description|Elementary particle, main constituent of matter}}
{{About|the elementary particle and its antiparticle}}
{{Featured article}}
{{Use dmy dates|date=April 2019}}
{{Use American English|date=April 2019}}
{{Infobox particle
| name            = Quark
| image           = <!-- Do not replace this image with the Y-shaped gluon flux tube without establishing consensus at [[WT:PHYS]] first, since this affects multiple articles, not just this one-->Quark structure proton.svg
| image_size      = 225px
| alt             = Three colored balls (symbolizing quarks) connected pairwise by springs (symbolizing gluons), all inside a gray circle (symbolizing a proton). The colors of the balls are red, green, and blue, to parallel each quark's color charge. The red and blue balls are labeled "u" (for "up" quark) and the green one is labeled "d" (for "down" quark).
| caption         = A [[proton]] is composed of two [[up quark]]s, one [[down quark]], and the [[gluons]] that mediate the forces "binding" them together. The [[Color charge|color assignment]] of individual quarks is arbitrary, but all three colors must be present; red, blue and green are used as an analogy to the primary colors that together produce a white color.
| num_types       = 6 ([[up quark|up]], [[down quark|down]], [[strange quark|strange]], [[charm quark|charm]], [[bottom quark|bottom]], and [[top quark|top]])<!-- mass/discovery order-->
| composition     = [[elementary particle]]
| statistics      = [[fermion]]ic
| group           =
| generation      = 1st, 2nd, 3rd 
| interaction     = [[Strong interaction|strong]], [[Weak interaction|weak]], [[Electromagnetic interaction|electromagnetic]], [[gravitation]]
| particle        =
| antiparticle    = antiquark ({{SubatomicParticle|Antiquark}})
| theorized       = {{plainlist|
* [[Murray Gell-Mann]] (1964) 
* [[George Zweig]] (1964)}}
| discovered      = [[SLAC National Accelerator Laboratory|SLAC]] ({{circa|1968}})
| symbol          = {{SubatomicParticle|Quark}}
| baryon_number   = {{sfrac|1|3}}
| mass            = 
| decay_time      =
| decay_particle  =
| electric_charge = +{{sfrac|2|3}}&nbsp;[[elementary charge|''e'']], −{{sfrac|1|3}}&nbsp;[[elementary charge|''e'']]
| color_charge    = yes
| spin            = {{sfrac|1|2}}&nbsp;[[reduced Planck constant|''ħ'']]
| num_spin_states =
}}

A '''quark''' ({{IPAc-en|k|w|ɔːr|k|,_|k|w|ɑːr|k|audio=LL-Q1860 (eng)-Naomi Persephone Amethyst (NaomiAmethyst)-quark.wav}}) is a type of [[elementary particle]] and a fundamental constituent of [[matter]]. Quarks combine to form [[composite particle]]s called [[hadron]]s, the most stable of which are [[proton]]s and [[neutron]]s, the components of [[atomic nucleus|atomic nuclei]].<ref>
{{cite encyclopedia
 |title=Quark (subatomic particle)
 |url=http://www.britannica.com/EBchecked/topic/486323/quark
 |encyclopedia=[[Encyclopædia Britannica]]
 |access-date=2008-06-29
}}</ref> All commonly observable matter is composed of up quarks, down quarks and [[electron]]s. Owing to a phenomenon known as ''[[color confinement]]'', quarks are never found in isolation; they can be found only within hadrons, which include [[baryon]]s (such as protons and neutrons) and [[meson]]s, or in [[quark–gluon plasma]]s.<ref name="HyperphysicsConfinment">
{{cite web
 |author=R. Nave
 |title=Confinement of Quarks
 |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/quark.html#c6
 |work=[[HyperPhysics]]
 |publisher=[[Georgia State University]], Department of Physics and Astronomy
 |access-date=2008-06-29
}}</ref><ref name="HyperphysicsBagModel">
{{cite web
 |author=R. Nave
 |title=Bag Model of Quark Confinement
 |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/qbag.html#c1
 |work=[[HyperPhysics]]
 |publisher=[[Georgia State University]], Department of Physics and Astronomy
 |access-date=2008-06-29
}}</ref><ref group="nb>There is also the theoretical possibility of [[#Other_phases_of_quark_matter|more exotic phases of quark matter]].</ref> For this reason, much of what is known about quarks has been drawn from observations of hadrons.

Quarks have various [[Intrinsic and extrinsic properties|intrinsic]] [[physical property|properties]], including [[electric charge]], [[mass]], [[color charge]], and [[Spin (physics)|spin]]. They are the only elementary particles in the [[Standard Model]] of [[particle physics]] to experience all four [[fundamental interaction]]s, also known as ''fundamental forces'' ([[electromagnetism]], [[gravitation]], [[strong interaction]], and [[weak interaction]]), as well as the only known particles whose electric charges are not [[integer]] multiples of the [[elementary charge]].

There are six types, known as ''[[flavour (particle physics)|flavors]]'', of quarks: [[Up quark|up]], [[Down quark|down]], [[Charm quark|charm]], [[Strange quark|strange]], [[Top quark|top]], and [[Bottom quark|bottom]].<ref name="HyperphysicsQuark">
{{cite web
 |author=R. Nave
 |title=Quarks
 |url=http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/quark.html
 |work=[[HyperPhysics]]
 |publisher=[[Georgia State University]], Department of Physics and Astronomy
 |access-date=2008-06-29
}}</ref> Up and down quarks have the lowest [[mass]]es of all quarks. The heavier quarks rapidly change into up and down quarks through a process of [[particle decay]]: the transformation from a higher mass state to a lower mass state. Because of this, up and down quarks are generally stable and the most common in the [[universe]], whereas strange, charm, bottom, and top quarks can only be produced in [[high energy physics|high energy]] collisions (such as those involving [[cosmic ray]]s and in [[particle accelerator]]s). For every quark flavor there is a corresponding type of [[antiparticle]], known as an '''antiquark''', that differs from the quark only in that some of its properties (such as the electric charge) have [[additive inverse|equal magnitude but opposite sign]].

The [[quark model]] was independently proposed by physicists [[Murray Gell-Mann]] and [[George Zweig]] in 1964.<ref name="Carithers">
{{cite journal
 |author1=B. Carithers
 |author2=P. Grannis
 |title=Discovery of the Top Quark
 |url=http://www.slac.stanford.edu/pubs/beamline/25/3/25-3-carithers.pdf
 |journal=[[Beam Line (journal)|Beam Line]]
 |volume=25 |issue=3 |pages=4–16
 |year=1995
 |access-date=2008-09-23
}}</ref> Quarks were introduced as parts of an ordering scheme for hadrons, and there was little evidence for their physical existence until [[deep inelastic scattering]] experiments at the [[SLAC National Accelerator Laboratory|Stanford Linear Accelerator Center]] in 1968.<ref name="Bloom">
{{cite journal
 |author=E. D. Bloom
 |display-authors=etal
 |title=High-Energy Inelastic ''e''–''p'' Scattering at 6° and 10°
 |journal=[[Physical Review Letters]]
 |volume=23 |issue=16 |pages=930–934
 |year=1969
 |bibcode=1969PhRvL..23..930B
 |doi=10.1103/PhysRevLett.23.930
 |doi-access=free
}}</ref><ref name="Breidenbach">
{{cite journal
 |author=M. Breidenbach
 |display-authors=etal
 |title=Observed Behavior of Highly Inelastic Electron–Proton Scattering
 |journal=[[Physical Review Letters]]
 |volume=23 |issue=16 |pages=935–939
 |year=1969
 |bibcode=1969PhRvL..23..935B
 |doi=10.1103/PhysRevLett.23.935
 |osti=1444731
 |s2cid=2575595
}}</ref> Accelerator program experiments have provided evidence for all six flavors. The top quark, first observed at [[Fermilab]] in 1995, was the last to be discovered.<ref name="Carithers"/>