The up quark or u quark (symbol: u) is the lightest of all quarks, a type of elementary particle, and a significant constituent of matter. It, along with the down quark, forms the neutrons (one up quark, two down quarks) and protons (two up quarks, one down quark) of atomic nuclei. It is part of the first generation of matter, has an electric charge of +2/3 e and a bare mass of 2.2+0.5
−0.4 MeV/c2. Like all quarks, the up quark is an elementary fermion with spin 1/2, and experiences all four fundamental interactions: gravitation, electromagnetism, weak interactions, and strong interactions. 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 charge have equal magnitude but opposite sign.
| Composition | elementary particle |
|---|---|
| Statistics | fermionic |
| Family | quark |
| Generation | first |
| Interactions | strong, weak, electromagnetic, gravity |
| Symbol | u |
| Antiparticle | up antiquark ( u ) |
| Theorized | Murray Gell-Mann (1964) George Zweig (1964) |
| Discovered | SLAC (1968) |
| Mass | 2.2+0.5 −0.4 MeV/c2 |
| Decays into | stable or down quark + positron + electron neutrino |
| Electric charge | +2/3 e |
| Color charge | Yes |
| Spin | 1/2 ħ |
| Weak isospin | LH: +1/2, RH: 0 |
| Weak hypercharge | LH: +1/3, RH: +4/3 |
Its existence (along with that of the down and strange quarks) was postulated in 1964 by Murray Gell-Mann and George Zweig to explain the Eightfold Way classification scheme of hadrons. The up quark was first observed by experiments at the Stanford Linear Accelerator Center in 1968.
History
In the beginnings of particle physics (first half of the 20th century), hadrons such as protons, neutrons and pions were thought to be elementary particles. 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 and Yuval Ne'eman (independently of each other) proposed a hadron classification scheme called the Eightfold Way, or in more technical terms, SU(3) flavor symmetry.
This classification scheme organized the hadrons into isospin multiplets, but the physical basis behind it was still unclear. In 1964, Gell-Mann and George Zweig (independently of each other) proposed the quark model, then consisting only of up, down, and strange quarks. 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.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).
At first people were reluctant to describe the three bodies as quarks, instead preferring Richard Feynman's parton description, but over time the quark theory became accepted (see November Revolution).
Mass
Despite being extremely common, the bare mass of the up quark is not well determined, but probably lies between 1.8 and 3.0 MeV/c2.Lattice QCD calculations give a more precise value: 2.01±0.14 MeV/c2.
When found in mesons (particles made of one quark and one antiquark) or baryons (particles made of three quarks), the 'effective mass' (or 'dressed' mass) of quarks becomes greater because of the binding energy caused by the 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
- M. Tanabashi et al. (Particle Data Group) (2018). "Review of Particle Physics". Physical Review D. 98 (3): 1–708. Bibcode:2018PhRvD..98c0001T. doi:10.1103/PhysRevD.98.030001. hdl:10044/1/68623. PMID 10020536.
- M. Gell-Mann (2000) [1964]. "The Eightfold Way: A theory of strong interaction symmetry". In M. Gell-Mann, Y. Ne'eman (ed.). The Eightfold Way. Westview Press. p. 11. ISBN 978-0-7382-0299-0.
Original: M. Gell-Mann (1961). "The Eightfold Way: A theory of strong interaction symmetry". Synchrotron Laboratory Report CTSL-20. California Institute of Technology. - Y. Ne'eman (2000) [1964]. "Derivation of strong interactions from gauge invariance". In M. Gell-Mann, Y. Ne'eman (ed.). The Eightfold Way. Westview Press. ISBN 978-0-7382-0299-0.
Original Y. Ne'eman (1961). "Derivation of strong interactions from gauge invariance". Nuclear Physics. 26 (2): 222–229. Bibcode:1961NucPh..26..222N. doi:10.1016/0029-5582(61)90134-1. - M. Gell-Mann (1964). "A Schematic Model of Baryons and Mesons". Physics Letters. 8 (3): 214–215. Bibcode:1964PhL.....8..214G. doi:10.1016/S0031-9163(64)92001-3.
- G. Zweig (1964). "An SU(3) Model for Strong Interaction Symmetry and its Breaking". Cern-Th-401. doi:10.17181/CERN-TH-401.
- G. Zweig (1964). "An SU(3) Model for Strong Interaction Symmetry and its Breaking: II". Cern-Th-412. doi:10.17181/CERN-TH-412.
- B. Carithers, P. Grannis (1995). "Discovery of the Top Quark" (PDF). . 25 (3): 4–16. Retrieved 2008-09-23.
- Bloom, E. D.; Coward, D.; Destaebler, H.; Drees, J.; Miller, G.; Mo, L.; Taylor, R.; Breidenbach, M.; et al. (1969). "High-Energy Inelastic e–p Scattering at 6° and 10°". Physical Review Letters. 23 (16): 930–934. Bibcode:1969PhRvL..23..930B. doi:10.1103/PhysRevLett.23.930.
- M. Breidenbach; Friedman, J.; Kendall, H.; Bloom, E.; Coward, D.; Destaebler, H.; Drees, J.; Mo, L.; Taylor, R.; et al. (1969). "Observed Behavior of Highly Inelastic Electron–Proton Scattering". Physical Review Letters. 23 (16): 935–939. Bibcode:1969PhRvL..23..935B. doi:10.1103/PhysRevLett.23.935. OSTI 1444731. S2CID 2575595.
- J. I. Friedman. "The Road to the Nobel Prize". Hue University. Archived from the original on 2008-12-25. Retrieved 2008-09-29.
- R. P. Feynman (1969). "Very High-Energy Collisions of Hadrons" (PDF). Physical Review Letters. 23 (24): 1415–1417. Bibcode:1969PhRvL..23.1415F. doi:10.1103/PhysRevLett.23.1415.
- S. Kretzer; Lai, H.; Olness, Fredrick; Tung, W.; et al. (2004). "CTEQ6 Parton Distributions with Heavy Quark Mass Effects". Physical Review D. 69 (11): 114005. arXiv:hep-ph/0307022. Bibcode:2004PhRvD..69k4005K. doi:10.1103/PhysRevD.69.114005. S2CID 119379329.
- D. J. Griffiths (1987). Introduction to Elementary Particles. John Wiley & Sons. p. 42. ISBN 978-0-471-60386-3.
- M. E. Peskin, D. V. Schroeder (1995). An introduction to quantum field theory. Addison–Wesley. p. 556. ISBN 978-0-201-50397-5.
- J. Beringer (Particle Data Group); et al. (2012). "PDGLive Particle Summary 'Quarks (u, d, s, c, b, t, b', t', Free)'" (PDF). Particle Data Group. Retrieved 2013-02-21.
- Cho, Adrian (April 2010). "Mass of the Common Quark Finally Nailed Down". Science Magazine.
Further reading
- A. Ali, G. Kramer; Kramer (2011). "JETS and QCD: A historical review of the discovery of the quark and gluon jets and its impact on QCD". European Physical Journal H. 36 (2): 245. arXiv:1012.2288. Bibcode:2011EPJH...36..245A. doi:10.1140/epjh/e2011-10047-1. S2CID 54062126.
- R. Nave. "Quarks". HyperPhysics. Georgia State University, Department of Physics and Astronomy. Retrieved 2008-06-29.
- A. Pickering (1984). Constructing Quarks. University of Chicago Press. pp. 114–125. ISBN 978-0-226-66799-7.
The up quark or u quark symbol u is the lightest of all quarks a type of elementary particle and a significant constituent of matter It along with the down quark forms the neutrons one up quark two down quarks and protons two up quarks one down quark of atomic nuclei It is part of the first generation of matter has an electric charge of 2 3 e and a bare mass of 2 2 0 5 0 4 MeV c2 Like all quarks the up quark is an elementary fermion with spin 1 2 and experiences all four fundamental interactions gravitation electromagnetism weak interactions and strong interactions 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 charge have equal magnitude but opposite sign Up quarkCompositionelementary particleStatisticsfermionicFamilyquarkGenerationfirstInteractionsstrong weak electromagnetic gravitySymboluAntiparticleup antiquark u TheorizedMurray Gell Mann 1964 George Zweig 1964 DiscoveredSLAC 1968 Mass2 2 0 5 0 4 MeV c2Decays intostable or down quark positron electron neutrinoElectric charge 2 3 eColor chargeYesSpin 1 2 ħWeak isospinLH 1 2 RH 0Weak hyperchargeLH 1 3 RH 4 3 Its existence along with that of the down and strange quarks was postulated in 1964 by Murray Gell Mann and George Zweig to explain the Eightfold Way classification scheme of hadrons The up quark was first observed by experiments at the Stanford Linear Accelerator Center in 1968 HistoryIn the beginnings of particle physics first half of the 20th century hadrons such as protons neutrons and pions were thought to be elementary particles 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 and Yuval Ne eman independently of each other proposed a hadron classification scheme called the Eightfold Way or in more technical terms SU 3 flavor symmetry This classification scheme organized the hadrons into isospin multiplets but the physical basis behind it was still unclear In 1964 Gell Mann and George Zweig independently of each other proposed the quark model then consisting only of up down and strange quarks 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 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 At first people were reluctant to describe the three bodies as quarks instead preferring Richard Feynman s parton description but over time the quark theory became accepted see November Revolution MassDespite being extremely common the bare mass of the up quark is not well determined but probably lies between 1 8 and 3 0 MeV c2 Lattice QCD calculations give a more precise value 2 01 0 14 MeV c2 When found in mesons particles made of one quark and one antiquark or baryons particles made of three quarks the effective mass or dressed mass of quarks becomes greater because of the binding energy caused by the 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 alsoDown quark Isospin Quark model Quantum MechanicsReferencesM Tanabashi et al Particle Data Group 2018 Review of Particle Physics Physical Review D 98 3 1 708 Bibcode 2018PhRvD 98c0001T doi 10 1103 PhysRevD 98 030001 hdl 10044 1 68623 PMID 10020536 M Gell Mann 2000 1964 The Eightfold Way A theory of strong interaction symmetry In M Gell Mann Y Ne eman ed The Eightfold Way Westview Press p 11 ISBN 978 0 7382 0299 0 Original M Gell Mann 1961 The Eightfold Way A theory of strong interaction symmetry Synchrotron Laboratory Report CTSL 20 California Institute of Technology Y Ne eman 2000 1964 Derivation of strong interactions from gauge invariance In M Gell Mann Y Ne eman ed The Eightfold Way Westview Press ISBN 978 0 7382 0299 0 Original Y Ne eman 1961 Derivation of strong interactions from gauge invariance Nuclear Physics 26 2 222 229 Bibcode 1961NucPh 26 222N doi 10 1016 0029 5582 61 90134 1 M Gell Mann 1964 A Schematic Model of Baryons and Mesons Physics Letters 8 3 214 215 Bibcode 1964PhL 8 214G doi 10 1016 S0031 9163 64 92001 3 G Zweig 1964 An SU 3 Model for Strong Interaction Symmetry and its Breaking Cern Th 401 doi 10 17181 CERN TH 401 G Zweig 1964 An SU 3 Model for Strong Interaction Symmetry and its Breaking II Cern Th 412 doi 10 17181 CERN TH 412 B Carithers P Grannis 1995 Discovery of the Top Quark PDF 25 3 4 16 Retrieved 2008 09 23 Bloom E D Coward D Destaebler H Drees J Miller G Mo L Taylor R Breidenbach M et al 1969 High Energy Inelastic e p Scattering at 6 and 10 Physical Review Letters 23 16 930 934 Bibcode 1969PhRvL 23 930B doi 10 1103 PhysRevLett 23 930 M Breidenbach Friedman J Kendall H Bloom E Coward D Destaebler H Drees J Mo L Taylor R et al 1969 Observed Behavior of Highly Inelastic Electron Proton Scattering Physical Review Letters 23 16 935 939 Bibcode 1969PhRvL 23 935B doi 10 1103 PhysRevLett 23 935 OSTI 1444731 S2CID 2575595 J I Friedman The Road to the Nobel Prize Hue University Archived from the original on 2008 12 25 Retrieved 2008 09 29 R P Feynman 1969 Very High Energy Collisions of Hadrons PDF Physical Review Letters 23 24 1415 1417 Bibcode 1969PhRvL 23 1415F doi 10 1103 PhysRevLett 23 1415 S Kretzer Lai H Olness Fredrick Tung W et al 2004 CTEQ6 Parton Distributions with Heavy Quark Mass Effects Physical Review D 69 11 114005 arXiv hep ph 0307022 Bibcode 2004PhRvD 69k4005K doi 10 1103 PhysRevD 69 114005 S2CID 119379329 D J Griffiths 1987 Introduction to Elementary Particles John Wiley amp Sons p 42 ISBN 978 0 471 60386 3 M E Peskin D V Schroeder 1995 An introduction to quantum field theory Addison Wesley p 556 ISBN 978 0 201 50397 5 J Beringer Particle Data Group et al 2012 PDGLive Particle Summary Quarks u d s c b t b t Free PDF Particle Data Group Retrieved 2013 02 21 Cho Adrian April 2010 Mass of the Common Quark Finally Nailed Down Science Magazine Further readingA Ali G Kramer Kramer 2011 JETS and QCD A historical review of the discovery of the quark and gluon jets and its impact on QCD European Physical Journal H 36 2 245 arXiv 1012 2288 Bibcode 2011EPJH 36 245A doi 10 1140 epjh e2011 10047 1 S2CID 54062126 R Nave Quarks HyperPhysics Georgia State University Department of Physics and Astronomy Retrieved 2008 06 29 A Pickering 1984 Constructing Quarks University of Chicago Press pp 114 125 ISBN 978 0 226 66799 7
