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 mean lifetime of . Properties
The most common decay modes of the  meson are  at ,  at , and various indistinguishable combinations of s 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, it is suppressed by the OZI rule. The quark composition of the  meson can be thought of as a mix between , , and  states, but it is very nearly a pure  state. This can be shown by deconstructing the wave function of the  into its component parts. We see that the  and  mesons are mixtures of the SU(3) wave functions as follows. ,
 ,

where
  is the nonet mixing angle,
  and
 . The mixing angle at which the components decouple completely can be calculated to be . The mixing angle of the  and  states is calculated from the masses of each state to be about 35˚, which is very close to maximum decoupling. Therefore, the  meson is nearly a pure  state. History
The existence of the  meson was first proposed by the Japanese American particle physicist, J. J. Sakurai, in 1962 as a resonance state between the  and the . It was discovered later in 1962 by P.L. Connolly, et al. in a 20-inch hydrogen bubble chamber at the Alternating Gradient Synchrotron (AGS) in Brookhaven National Laboratory in Uptown, NY while they were studying  collisions at approximately 2.23GeV/c. In essence, the reaction involved a beam of s being accelerated to high energies to collide with protons. The  meson has several possible decay modes. The most energetically favored mode involves the  meson decaying into 3 pions, which is what would naïvely be expected. However, we instead observe that it decays most frequently into 2 kaons. Between 1963 and 1966, 3 people, Susumu Okubo, George Zweig and Jugoro Iizuka, each independently proposed a rule to account for the observed suppression of the 3 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  and  mesons. Namely, on average they last  and  respectively. This is compared to the normal mean lifetime of a meson decaying via the strong force, which is on the order of . In 1999, a  factory named DAFNE (or DANE since the F stands for " Factory") began operation to study the decay of the  meson in Frascati, Italy. It produces  mesons via electron-positron collisions. It has numerous detectors, including the KLOE detector which was in operation at the beginning of its operation. See also
Charmonium
List of mesons
List of particles
Quark model

References

Mesons
Onia
Strange quark
Subatomic particles with spin 1