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{{Short description|Principle in hadron decay rates}} |
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The '''OZI rule''' is part of [[Quantum chromodynamics|QCD]] which explains why certain [[Particle decay|decay mode]]s appear less frequently than otherwise might be expected. It was independently proposed by Susumu Okubo, [[George Zweig]] and Jugoro Iizuka in the 1960s. It states that any [[Strong interaction|strongly]] occurring process with a [[Feynman diagram|Feynman Diagram]] that can be split in two by cutting only internal [[gluon]] lines will be suppressed. |
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| header = OZI rule |
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| image1 = OZI rule - Feynmann diagram2.svg |
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| caption1 = Decay of the [[Phi meson]] into three [[pion]]s is suppressed by the OZI rule. |
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| image2 = OZI rule - Feynmann diagram.svg |
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| caption2 =Decay of the [[Phi meson]] into two [[Kaon]]s is not suppressed by the OZI rule. |
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The '''Okubo–Zweig–Iizuka rule''' or '''OZI rule''' is a consequence of [[quantum chromodynamics]] (QCD) that explains why certain [[Particle decay|decay modes]] appear less frequently than otherwise might be expected. It was independently proposed by [[Susumu Okubo]], [[George Zweig]] and [[Jugoro Iizuka]] in the 1960s.<ref>{{cite journal |last=Okubo |first=S. |title=φ-meson and unitary symmetry model |journal=Physics Letters |publisher=Elsevier BV |volume=5 |issue=2 |year=1963 |issn=0031-9163 |doi=10.1016/s0375-9601(63)92548-9 |pages=165–168|bibcode=1963PhL.....5..165O }}</ref><ref>{{cite report |first=G. |last=Zweig |title=CERN Report No. 8419 / TH412 |year=1964}}</ref><ref>{{cite journal |last=Iizuka |first=Jugoro |title=A Systematics and Phenomenology of Meson Family |journal=Progress of Theoretical Physics Supplement |publisher=Oxford University Press (OUP) |volume=37 |year=1966 |issn=0375-9687 |doi=10.1143/ptps.37.21 |pages=21–34 |doi-access=free|bibcode=1966PThPS..37...21I }}</ref> |
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It states that any [[Strong interaction|strongly]] occurring process will be suppressed if, through only the removal of internal [[gluon]] lines, its [[Feynman diagram]] can be separated into two disconnected diagrams: one containing all of the initial-state particles and one containing all of the final-state particles. |
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An example of such a suppressed decay is |
An example of such a suppressed decay is the [[Phi meson]] into [[pion]]s: {{nowrap| φ → π<sup>+</sup> + π<sup>−</sup> + π<sup>0</sup> .}} It would be expected that this decay mode would dominate over other decay modes such as {{nowrap| φ → K<sup>+</sup> + K<sup>−</sup> ,}} which have much lower [[Q value (nuclear science)|{{mvar|Q}} values]]. In actuality, it is seen that [[Phi meson|φ]] decays to [[kaon]]s 84% of the time, suggesting the decay path to [[pion]]s is suppressed. |
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An explanation of the OZI rule can be seen from the |
An explanation of the OZI rule can be seen from the decrease of the [[Running coupling|coupling constant]] in [[Quantum chromodynamics|QCD]] with increasing energy (or [[momentum transfer]]). For the OZI suppressed channels, the gluons must have high {{mvar|q}}<sup>2</sup> (at least as much as the [[rest mass]] energies of the quarks into which they decay) and so the coupling constant will appear small to these gluons. |
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Another explanation of the OZI rule comes from the [[1/N_expansion|large-{{mvar|N}}{{sub|c}}]] limit, in which the number of [[Color charge|colors]] {{mvar|N}}{{sub|c}} is assumed to be infinite. The OZI suppressed processes have a higher ratio of vertices (which contribute factors of {{frac|1|{{mvar|N}}{{sub|c}}}}) to independent fermion loops (which contribute factors of {{mvar|N}}{{sub|c}}) when compared to the non-suppressed processes, and so these processes are much less common. |
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* [[Charmonium]] |
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A further example is given by the decays of excited states of [[charmonium]] (bound state of charm quark and antiquark). |
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== Notes and references == |
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For states lighter than the charged [[D meson]]s, the decay must proceed just like the above example into three [[pion]]s, with three virtual gluons mediating the interaction, each of which must have enough energy to produce a quark-antiquark pair. |
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<references/> |
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But above the [[D meson]] threshold, the original valence quarks need not annihilate; they can propagate into the final states. In this case, only two gluons are required, which share the energy of the light quark-antiquark pair that is spontaneously nucleated. They are thus lower in energy than the three gluons of the OZI-suppressed annihilation. The suppression arises from both the smaller values of the QCD coupling constant at high energies, as well as the greater number of interaction vertices. |
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== References == |
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{{Uncategorized|date=September 2010}} |
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{{reflist|25em}} |
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== Sources == |
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* {{cite book |first1=D. |last1=Griffiths |title=Introduction to Elementary Particles |publisher=Wiley-VCH |place=Germany |edition=2nd |year=2008 |at=§5.4.1 |isbn=978-3-527-40601-2}} |
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[[Category:Quantum chromodynamics]] |
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[[de:OZI-Regel]] |
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Latest revision as of 20:00, 26 September 2024
The Okubo–Zweig–Iizuka rule or OZI rule is a consequence of quantum chromodynamics (QCD) that explains why certain decay modes appear less frequently than otherwise might be expected. It was independently proposed by Susumu Okubo, George Zweig and Jugoro Iizuka in the 1960s.[1][2][3] It states that any strongly occurring process will be suppressed if, through only the removal of internal gluon lines, its Feynman diagram can be separated into two disconnected diagrams: one containing all of the initial-state particles and one containing all of the final-state particles.
An example of such a suppressed decay is the Phi meson into pions: φ → π+ + π− + π0 . It would be expected that this decay mode would dominate over other decay modes such as φ → K+ + K− , which have much lower Q values. In actuality, it is seen that φ decays to kaons 84% of the time, suggesting the decay path to pions is suppressed.
An explanation of the OZI rule can be seen from the decrease of the coupling constant in QCD with increasing energy (or momentum transfer). For the OZI suppressed channels, the gluons must have high q2 (at least as much as the rest mass energies of the quarks into which they decay) and so the coupling constant will appear small to these gluons.
Another explanation of the OZI rule comes from the large-Nc limit, in which the number of colors Nc is assumed to be infinite. The OZI suppressed processes have a higher ratio of vertices (which contribute factors of 1⁄Nc) to independent fermion loops (which contribute factors of Nc) when compared to the non-suppressed processes, and so these processes are much less common.
A further example is given by the decays of excited states of charmonium (bound state of charm quark and antiquark). For states lighter than the charged D mesons, the decay must proceed just like the above example into three pions, with three virtual gluons mediating the interaction, each of which must have enough energy to produce a quark-antiquark pair.
But above the D meson threshold, the original valence quarks need not annihilate; they can propagate into the final states. In this case, only two gluons are required, which share the energy of the light quark-antiquark pair that is spontaneously nucleated. They are thus lower in energy than the three gluons of the OZI-suppressed annihilation. The suppression arises from both the smaller values of the QCD coupling constant at high energies, as well as the greater number of interaction vertices.
See also
[edit]References
[edit]- ^ Okubo, S. (1963). "φ-meson and unitary symmetry model". Physics Letters. 5 (2). Elsevier BV: 165–168. Bibcode:1963PhL.....5..165O. doi:10.1016/s0375-9601(63)92548-9. ISSN 0031-9163.
- ^ Zweig, G. (1964). CERN Report No. 8419 / TH412 (Report).
- ^ Iizuka, Jugoro (1966). "A Systematics and Phenomenology of Meson Family". Progress of Theoretical Physics Supplement. 37. Oxford University Press (OUP): 21–34. Bibcode:1966PThPS..37...21I. doi:10.1143/ptps.37.21. ISSN 0375-9687.
Sources
[edit]- Martin, B.R.; Shaw, G. (1997). "§6.1.1 Charmonium". Particle physics (2nd ed.). Chichester, UK: John Wiley & Sons. p. 128. ISBN 0-471-92358-3.
- Griffiths, D. (2008). Introduction to Elementary Particles (2nd ed.). Germany: Wiley-VCH. §5.4.1. ISBN 978-3-527-40601-2.
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