Phi meson

File:Quark structure phi meson.svg

Quark structure of the phi meson, is a vector meson formed of a strange quark and a strange antiquark.

In particle physics, the phi meson or Template:Subatomic particle meson is a vector meson formed of a strange quark and a strange antiquark. It was the Template:Subatomic particle meson's unexpected propensity to decay into

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Template:Rcatsh and

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Template:Rcatsh that led to the discovery of the OZI rule. It has a mass of and a mean lifetime of 1.55±0.01 × Template:10^ s .

Properties

The most common decay modes of the Template:Subatomic particle meson are Template:Subatomic particleTemplate:Subatomic particle at , Template:Subatomic particle+Template:Subatomic particle at , and various indistinguishable mixed combinations of rho mesons and pions at . In all cases, it decays via the strong force. The pion channel would naïvely be the dominant decay channel because the collective mass of the pions is smaller than that of the kaons, making it energetically favorable; however, that decay route is suppressed by the OZI rule.

Technically, the quark composition of the Template:Subatomic particle meson can be thought of as a mix between Template:Subatomic particleTemplate:Subatomic particle, Template:Subatomic particleTemplate:Subatomic particle, and Template:Subatomic particleTemplate:Subatomic particle states, but it is very nearly a pure Template:Subatomic particleTemplate:Subatomic particle state. This can be shown by deconstructing the wave function of the Template:Subatomic particle into its component parts. We see that the Template:Subatomic particle and Template:Subatomic particle mesons are mixtures of the SU(3) wave functions as follows.

$\varphi ={\psi }_8\cos \theta -{\psi }_1\sin \theta$,

$\omega ={\psi }_8\sin \theta +{\psi }_1\cos \theta$,

where

$\theta$ is the nonet mixing angle,

${\psi }_8=\frac{u\bar{u}+d\bar{d}-2s\bar{s}}{\sqrt{6}}$ and

${\psi }_1=\frac{u\bar{u}+d\bar{d}+s\bar{s}}{\sqrt{3}}.$

The mixing angle at which the components decouple completely can be calculated to be $\arctan \frac{1}{\sqrt{2}}\approx 35.3^{\circ }.$ The mixing angle of the Template:Subatomic particle and Template:Subatomic particle states is calculated from the masses of each state to be about 35˚, which is very close to maximum decoupling. Therefore, the Template:Subatomic particle meson is nearly a pure Template:Subatomic particleTemplate:Subatomic particle state.

History

The existence of the Template:Subatomic particle meson was first proposed by the Japanese American particle physicist, J. J. Sakurai, in 1962 as a resonance state between the

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Template:Rcatsh and the

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Template:Rcatsh. It was discovered later by Template:Harvp in a 20 inch hydrogen bubble chamber at the Alternating Gradient Synchrotron (AGS) in Brookhaven National Laboratory in Upton, NY while they were studying

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Template:RcatshTemplate:Subatomic particle collisions at approximately 2.23 GeV/Template:Mvar. In essence, the reaction involved a beam of

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Template:Rcatshs being accelerated to high energies to collide with protons.

The Template:Subatomic particle meson has several possible decay modes. The most energetically favored mode involves the Template:Subatomic particle meson decaying into three pions, which is what would naïvely be expected. However, we instead observe that it decays most frequently into two kaons. Between 1963 and 1966, three people, Susumu Okubo, George Zweig, and Jugoro Iizuka, each independently proposed a rule to account for the observed suppression of the three pion decay. This rule is now known as the OZI rule and is also the currently accepted explanation for the unusually long lifetimes of the Template:Subatomic particle and Template:Subatomic particle mesons. Namely, on average they last ~ 7 × Template:10^ s and ~ 1.5 × Template:10^ s respectively. This is compared to the normal mean lifetime of a meson decaying via the strong force, which is on the order of Template:10^ s .

In 1999, a Template:Subatomic particle factory named DAFNE (or DATemplate:Subatomic particleNE since the F stands for "Template:Subatomic particle Factory") began operation to study the decay of the Template:Subatomic particle meson in Frascati, Italy. It produces Template:Subatomic particle mesons via electron-positron collisions. It has numerous detectors, including the KLOE detector which was in operation at the beginning of its operation.

Particle name	Particle symbol	Antiparticle symbol	Quark content	Rest mass (MeV/c2)	IG	JPC	S	C	B'	Mean lifetime (s)	Commonly decays to (>5% of decays)
Phi meson	Template:Subatomic particle(1020)	Self	Template:Subatomic particleTemplate:Subatomic particle	1,019.461 ± 0.020	0−	1−−	0	0	0	1.55 ± 0.01 × Template:10^ [f]	Template:Subatomic particle + Template:Subatomic particle or Template:Subatomic particle + Template:Subatomic particle or (Template:Subatomic particle + Template:Subatomic particle) / (Template:Subatomic particle + Template:Subatomic particle + Template:Subatomic particle)

See also

• Charmonium
• List of mesons
• List of particles
• Quark model