The OZI rule is a consequence of

quantum chromodynamics In theoretical physics, quantum chromodynamics (QCD) is the theory of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a type ...

(QCD) that explains why certain decay modes appear less frequently than otherwise might be expected. It was independently proposed by

Susumu Okubo was a Japanese theoretical physicist at the University of Rochester. Ōkubo worked primarily on elementary particle physics. He is famous for the Gell-Mann–Okubo mass formula for mesons and baryons in the quark model; this formula correctly pre ...

George Zweig George Zweig (; born May 30, 1937) is a Russian-American physicist. He was trained as a particle physicist under Richard Feynman. He introduced, independently of Murray Gell-Mann, the quark model (although he named it "aces"). He later turned his ...

and Jugoro Iizuka in the 1960s. It states that any strongly occurring process will be suppressed if, through only the removal of internal

gluon A gluon ( ) is an elementary particle that acts as the exchange particle (or gauge boson) for the strong force between quarks. It is analogous to the exchange of photons in the electromagnetic force between two charged particles. Gluons bind q ...

lines, its

Feynman diagram In theoretical physics, a Feynman diagram is a pictorial representation of the mathematical expressions describing the behavior and interaction of subatomic particles. The scheme is named after American physicist Richard Feynman, who introduc ...

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 In particle physics, the phi meson or meson is a vector meson formed of a strange quark and a strange antiquark. It was the meson's unusual propensity to decay into and that led to the discovery of the OZI rule. It has a mass of and a mea ...

into

pion In particle physics, a pion (or a pi meson, denoted with the Greek letter pi: ) is any of three subatomic particles: , , and . Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the lightest mesons and, more gene ...

s: It would be expected that this decay mode would dominate over other decay modes such as which have much lower values. In actuality, it is seen that φ decays to

kaon KAON (Karlsruhe ontology) is an ontology infrastructure developed by the University of Karlsruhe and the Research Center for Information Technologies in Karlsruhe. Its first incarnation was developed in 2002 and supported an enhanced version of ...

s 84% of the time, suggesting the decay path to

s is suppressed. An explanation of the OZI rule can be seen from the decrease of the coupling constant in

QCD In theoretical physics, quantum chromodynamics (QCD) is the theory of the strong interaction between quarks mediated by gluons. Quarks are fundamental particles that make up composite hadrons such as the proton, neutron and pion. QCD is a ty ...

with increasing energy (or

momentum transfer In particle physics, wave mechanics and optics, momentum transfer is the amount of momentum that one particle gives to another particle. It is also called the scattering vector as it describes the transfer of wavevector in wave mechanics. In the s ...

). For the OZI suppressed channels, the gluons must have high ² (at least as much as the

rest mass The invariant mass, rest mass, intrinsic mass, proper mass, or in the case of bound systems simply mass, is the portion of the total mass of an object or system of objects that is independent of the overall motion of the system. More precisely, i ...

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- limit, in which the number of

colors Color (American English) or colour (British English) is the visual perceptual property deriving from the spectrum of light interacting with the photoreceptor cells of the eyes. Color categories and physical specifications of color are associa ...

is assumed to be infinite. The OZI suppressed processes have a higher ratio of vertices (which contribute factors of ) to independent fermion loops (which contribute factors of ) 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 In particle physics, quarkonium (from quark and -onium, pl. quarkonia) is a flavorless meson whose constituents are a heavy quark and its own antiquark, making it both a neutral particle and its own antiparticle. Light quarks Light quarks ( up ...

(bound state of charm quark and antiquark). For states lighter than the charged

D meson The D mesons are the lightest particle containing charm quarks. They are often studied to gain knowledge on the weak interaction. The strange D mesons (Ds) were called "F mesons" prior to 1986. Overview The D mesons were discovere ...

s, the decay must proceed just like the above example into three

s, with three virtual gluons mediating the interaction, each of which must have enough energy to produce a quark-antiquark pair. But above the

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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* * Quantum chromodynamics {{particle-stub

See also

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