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Up quark
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{{Short description|Type of quark}} {{Infobox Particle |bgcolour = |name = Up quark |image = |caption = |num_types = |composition = [[elementary particle]] |statistics = [[fermion]]ic |group = [[quark]] |generation = first |interaction = [[Strong interaction|strong]], [[Weak interaction|weak]], [[Electromagnetic interaction|electromagnetic]], [[gravity]] |particle = |antiparticle = up antiquark ({{SubatomicParticle|Up antiquark}}) |theorized = [[Murray Gell-Mann]] (1964){{br}}[[George Zweig]] (1964) |discovered = [[SLAC]] (1968) |symbol = {{SubatomicParticle|up quark}} |mass = {{val|2.2|+0.5|-0.4|ul=MeV/c2}}<ref name="PDG2018"> {{cite journal |author=M. Tanabashi et al. (Particle Data Group) |title=Review of Particle Physics |year= 2018 |doi=10.1103/PhysRevD.98.030001 |volume=98 |issue=3 |pages=1–708 |journal=Physical Review D |pmid=10020536 |url=http://pdglive.lbl.gov/DataBlock.action?node=Q123UM |doi-access=free |bibcode=2018PhRvD..98c0001T |hdl=10044/1/68623 |hdl-access=free }}</ref> |decay_time = |decay_particle = stable or [[down quark]] + [[positron]] + [[electron neutrino]] |electric_charge = +{{sfrac|2|3}} [[Elementary charge|''e'']] |color_charge = yes |spin = {{sfrac|1|2}} [[reduced Planck constant|''ħ'']] |num_spin_states = |weak_isospin = {{nowrap|[[Chirality (physics)|LH]]: +{{sfrac|1|2}}, [[Chirality (physics)|RH]]: 0}} |weak_hypercharge= {{nowrap|[[Chirality (physics)|LH]]: +{{sfrac|1|3}}, [[Chirality (physics)|RH]]: +{{sfrac|4|3}}}} }} The '''up quark''' or '''u quark''' (symbol: u) is the lightest of all [[quark]]s, a type of [[elementary particle]], and a significant constituent of [[matter]]. It, along with the [[down quark]], forms the [[neutron]]s (one up quark, two down quarks) and [[proton]]s (two up quarks, one down quark) of [[atomic nucleus|atomic nuclei]]. It is part of the [[generation (physics)|first generation]] of matter, has an [[electric charge]] of +{{sfrac|2|3}} [[elementary charge|''e'']] and a [[Quark#Mass|bare mass]] of {{val|2.2|+0.5|-0.4|ul=MeV/c2}}.<ref name="PDG2018"/> Like all [[quark]]s, the up quark is an [[elementary particle|elementary]] [[fermion]] with [[Spin (physics)|spin]] [[spin-1/2|{{sfrac|1|2}}]], and experiences all four [[fundamental interaction]]s: [[gravitation]], [[electromagnetism]], [[weak interaction]]s, and [[strong interaction]]s. The [[antiparticle]] of the up quark is the '''up antiquark''' (sometimes called ''antiup quark'' or simply ''antiup''), which differs from it only in that some of its properties, such as [[electric charge|charge]] have [[additive inverse|equal magnitude but opposite sign]]. Its existence (along with that of the [[down quark|down]] and [[strange quark]]s) was postulated in 1964 by [[Murray Gell-Mann]] and [[George Zweig]] to explain the [[Eightfold Way (physics)|Eightfold Way]] classification scheme of [[hadron]]s. The up quark was first observed by experiments at the [[Stanford Linear Accelerator Center]] in 1968. == History == {{Standard model of particle physics}} In the beginnings of particle physics (first half of the 20th century), [[hadrons]] such as [[proton]]s, [[neutron]]s and [[pion]]s were thought to be [[elementary particle]]s. However, as new hadrons were discovered, the '[[particle zoo]]' grew from a few particles in the early 1930s and 1940s to several dozens of them in the 1950s. The relationships between each of them were unclear until 1961, when [[Murray Gell-Mann]]<ref> {{cite book |author=M. Gell-Mann |year=2000 |orig-year=1964 |chapter=The Eightfold Way: A theory of strong interaction symmetry |editor=M. Gell-Mann, Y. Ne'eman |title=The Eightfold Way |page=11 |publisher=[[Westview Press]] |isbn=978-0-7382-0299-0 }}{{br}}Original:{{cite journal |author=M. Gell-Mann |year=1961 |title=The Eightfold Way: A theory of strong interaction symmetry |journal=Synchrotron Laboratory Report CTSL-20 |publisher=[[California Institute of Technology]] }}</ref> and [[Yuval Ne'eman]]<ref> {{cite book |author=Y. Ne'eman |year=2000 |orig-year=1964 |chapter=Derivation of strong interactions from gauge invariance |editor=M. Gell-Mann, Y. Ne'eman |title=The Eightfold Way |publisher=[[Westview Press]] |isbn=978-0-7382-0299-0 }}{{br}}Original {{cite journal |author=Y. Ne'eman |year=1961 |title=Derivation of strong interactions from gauge invariance |journal=[[Nuclear Physics (journal)|Nuclear Physics]] |volume=26 |pages=222–229 |doi=10.1016/0029-5582(61)90134-1 |bibcode = 1961NucPh..26..222N |issue=2 }}</ref> (independently of each other) proposed a hadron classification scheme called the [[Eightfold way (physics)|Eightfold Way]], or in more technical terms, [[SU(3)]] [[flavor symmetry]]. This classification scheme organized the hadrons into [[isospin|isospin multiplet]]s, but the physical basis behind it was still unclear. In 1964, Gell-Mann<ref name="Gell-Man1964"> {{cite journal |author=M. Gell-Mann |title=A Schematic Model of Baryons and Mesons |journal=[[Physics Letters]] |volume=8 |issue=3 |pages=214–215 |year=1964 |doi=10.1016/S0031-9163(64)92001-3 |bibcode=1964PhL.....8..214G }}</ref> and [[George Zweig]]<ref name="Zweig1964a"> {{cite journal |author=G. Zweig |title=An SU(3) Model for Strong Interaction Symmetry and its Breaking |journal=Cern-Th-401 |url=https://cds.cern.ch/record/352337 |year=1964 |doi=10.17181/CERN-TH-401 }}</ref><ref name="Zweig1964b"> {{cite journal |author=G. Zweig |title=An SU(3) Model for Strong Interaction Symmetry and its Breaking: II |journal=Cern-Th-412 |url=https://cds.cern.ch/record/570209 |year=1964 |doi=10.17181/CERN-TH-412 }}</ref> (independently of each other) proposed the [[quark model]], then consisting only of up, [[down quark|down]], and [[strange quark]]s.<ref name="Carithers"> {{cite journal |author=B. Carithers, 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> However, while the quark model explained the Eightfold Way, no direct evidence of the existence of quarks was found until 1968 at the [[Stanford Linear Accelerator Center]].<ref name="Bloom"> {{cite journal |last1=Bloom |first1=E. D. |title=High-Energy Inelastic ''e''–''p'' Scattering at 6° and 10° |journal=[[Physical Review Letters]] |volume=23 |issue=16 |pages=930–934 |year=1969 |doi=10.1103/PhysRevLett.23.930 |bibcode=1969PhRvL..23..930B |last2=Coward |first2=D. |last3=Destaebler |first3=H. |last4=Drees |first4=J. |last5=Miller |first5=G. |last6=Mo |first6=L. |last7=Taylor|first7=R. |last8=Breidenbach |first8=M. |last9=Friedman |first9=J. |last10=Hartmann |first10=G. |last11=Kendall |first11=H. |display-authors=8 |doi-access=free }}</ref><ref name="Breidenbach"> {{cite journal |author=M. Breidenbach |title=Observed Behavior of Highly Inelastic Electron–Proton Scattering |journal=[[Physical Review Letters]] |volume=23 |issue=16 |pages=935–939 |year=1969 |doi=10.1103/PhysRevLett.23.935 |bibcode=1969PhRvL..23..935B |last2=Friedman |first2=J. |last3=Kendall |first3=H. |last4=Bloom |first4=E. |last5=Coward |first5=D. |last6=Destaebler |first6=H. |last7=Drees |first7=J. |last8=Mo |first8=L. |last9=Taylor |first9=R. |osti=1444731 |s2cid=2575595 |display-authors=etal }}</ref> [[Deep inelastic scattering]] experiments indicated that protons had substructure, and that protons made of three more-fundamental particles explained the data (thus confirming the [[quark model]]).<ref> {{cite web |author = J. I. Friedman |title = The Road to the Nobel Prize |url = http://www.hueuni.edu.vn/hueuni/en/news_detail.php?NewsID=1606&PHPSESSID=909807ffc5b9c0288cc8d137ff063c72 |publisher = [[Hue University]] |access-date = 2008-09-29 |archive-url = https://web.archive.org/web/20081225093044/http://www.hueuni.edu.vn/hueuni/en/news_detail.php?NewsID=1606&PHPSESSID=909807ffc5b9c0288cc8d137ff063c72 |archive-date = 2008-12-25 |url-status = dead }}</ref> At first people were reluctant to describe the three bodies as quarks, instead preferring [[Richard Feynman]]'s [[parton (particle physics)|parton]] description,<ref> {{cite journal |author=R. P. Feynman |title=Very High-Energy Collisions of Hadrons |journal=[[Physical Review Letters]] |volume=23 |issue=24 |pages=1415–1417 |year=1969 |doi=10.1103/PhysRevLett.23.1415 |bibcode=1969PhRvL..23.1415F |url=http://authors.library.caltech.edu/3871/1/FEYprl69.pdf }}</ref><ref> {{cite journal |author=S. Kretzer |title=CTEQ6 Parton Distributions with Heavy Quark Mass Effects |journal=[[Physical Review D]] |volume=69 |issue=11 |page=114005 |year=2004 |doi=10.1103/PhysRevD.69.114005 |arxiv=hep-ph/0307022 |bibcode = 2004PhRvD..69k4005K |last2=Lai |first2=H. |last3=Olness |first3=Fredrick |last4=Tung |first4=W. |s2cid=119379329 |display-authors=etal }}</ref><ref name="Griffiths"> {{cite book |author=D. J. Griffiths |title=Introduction to Elementary Particles |page=42 |publisher=[[John Wiley & Sons]] |year=1987 |isbn=978-0-471-60386-3 }}</ref> but over time the quark theory became accepted (see ''[[November Revolution (physics)|November Revolution]]'').<ref> {{cite book |author=M. E. Peskin, D. V. Schroeder |year=1995 |title=An introduction to quantum field theory |url=https://archive.org/details/introductiontoqu0000pesk |url-access=registration |page=[https://archive.org/details/introductiontoqu0000pesk/page/556 556] |publisher=[[Addison–Wesley]] |isbn=978-0-201-50397-5 }}</ref> == Mass == Despite being extremely common, the [[Quark#Mass|bare mass]] of the up quark is not well determined, but probably lies between 1.8 and {{val|3.0|ul=MeV/c2}}.<ref name="PDG2012"> {{cite web |author=J. Beringer ([[Particle Data Group]]) |url=http://pdg.lbl.gov/2012/tables/rpp2012-sum-quarks.pdf |title=PDGLive Particle Summary 'Quarks (u, d, s, c, b, t, b′, t′, Free)' |publisher=[[Particle Data Group]] |year=2012 |access-date=2013-02-21 |display-authors=etal }}</ref> [[Lattice QCD]] calculations give a more precise value: {{val|2.01|0.14|ul=MeV/c2}}.<ref name=lqcd>{{cite web|last=Cho|first=Adrian|title=Mass of the Common Quark Finally Nailed Down|url=https://www.science.org/content/article/mass-common-quark-finally-nailed-down|publisher=Science Magazine|date=April 2010}}</ref> When found in [[meson]]s (particles made of one quark and one [[antiparticle|antiquark]]) or [[baryon]]s (particles made of three quarks), the 'effective mass' (or 'dressed' mass) of quarks [[Quark#Mass|becomes greater]] because of the [[Quantum chromodynamics binding energy|binding energy]] caused by the [[gluon|gluon field]] between each quark (see ''[[Mass–energy equivalence]]''). The bare mass of up quarks is so light, it cannot be straightforwardly calculated because relativistic effects have to be taken into account. == See also == * [[Down quark]] * [[Isospin]] * [[Quark model]] * [[Quantum Mechanics]] == References == {{reflist|30em}} == Further reading == * {{cite journal |author=A. Ali, G. Kramer |year=2011 |title=JETS and QCD: A historical review of the discovery of the quark and gluon jets and its impact on QCD |journal=[[European Physical Journal H]] |volume= 36|issue= 2|pages=245 |doi=10.1140/epjh/e2011-10047-1 |bibcode = 2011EPJH...36..245A |arxiv = 1012.2288 |last2=Kramer |s2cid=54062126 }} * {{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 }} * {{cite book |author=A. Pickering |title=Constructing Quarks |pages=114–125 |publisher=[[University of Chicago Press]] |year=1984 |isbn=978-0-226-66799-7 }} {{Particles}} {{Authority control}} {{DEFAULTSORT:Up Quark}} [[Category:Quarks]] [[Category:Elementary particles]]
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