
In
particle physics
Particle physics or high-energy physics is the study of Elementary particle, fundamental particles and fundamental interaction, forces that constitute matter and radiation. The field also studies combinations of elementary particles up to the s ...
, the phi meson or meson is a
vector
Vector most often refers to:
* Euclidean vector, a quantity with a magnitude and a direction
* Disease vector, an agent that carries and transmits an infectious pathogen into another living organism
Vector may also refer to:
Mathematics a ...
meson
In particle physics, a meson () is a type of hadronic subatomic particle composed of an equal number of quarks and antiquarks, usually one of each, bound together by the strong interaction. Because mesons are composed of quark subparticles, the ...
formed of a
strange
Strange may refer to:
Fiction
* Strange (comic book), a comic book limited series by Marvel Comics
* Strange (Marvel Comics), one of a pair of Marvel Comics characters known as The Strangers
* Adam Strange, a DC Comics superhero
* The title c ...
quark
A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nucleus, atomic nuclei ...
and a
strange
Strange may refer to:
Fiction
* Strange (comic book), a comic book limited series by Marvel Comics
* Strange (Marvel Comics), one of a pair of Marvel Comics characters known as The Strangers
* Adam Strange, a DC Comics superhero
* The title c ...
antiquark
A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. All commonly ...
. It was the meson's unexpected 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 mixed combinations of
rho meson
In particle physics, a rho meson is a short-lived hadronic particle that is an isospin triplet whose three states are denoted as , and . Along with pions and omega mesons, the rho meson carries the nuclear force within the atomic nucleus. Afte ...
s and
pions
In particle physics, a pion (, ) or 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, mo ...
at .
In all cases, it decays via the
strong force
In nuclear physics and particle physics, the strong interaction, also called the strong force or strong nuclear force, is one of the four known fundamental interactions. It confines quarks into protons, neutrons, and other hadron particles, an ...
. 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 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
In quantum physics, a wave function (or wavefunction) is a mathematical description of the quantum state of an isolated quantum system. The most common symbols for a wave function are the Greek letters and (lower-case and capital psi (letter) ...
of the into its component parts. We see that the and mesons are mixtures of the
SU(3)
In mathematics, the special unitary group of degree , denoted , is the Lie group of unitary matrices with determinant 1.
The matrices of the more general unitary group may have complex determinants with absolute value 1, rather than real 1 i ...
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 by in a 20 inch hydrogen bubble chamber at the
Alternating Gradient Synchrotron (AGS) in
Brookhaven National Laboratory
Brookhaven National Laboratory (BNL) is a United States Department of Energy national laboratories, United States Department of Energy national laboratory located in Upton, New York, a hamlet of the Brookhaven, New York, Town of Brookhaven. It w ...
in
Upton, NY while they were studying collisions at approximately 2.23 GeV/.
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 three
pions
In particle physics, a pion (, ) or 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, mo ...
, 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
George Zweig (; born May 30, 1937) is an American physicist of Russian-Jewish origin. 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"). ...
, 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 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
Frascati () is a city and in the Metropolitan City of Rome Capital in the Lazio region of central Italy. It is located south-east of Rome, on the Alban Hills close to the ancient city of Tusculum. Frascati is closely associated with science, ...
, Italy
Italy, officially the Italian Republic, is a country in Southern Europe, Southern and Western Europe, Western Europe. It consists of Italian Peninsula, a peninsula that extends into the Mediterranean Sea, with the Alps on its northern land b ...
.[ It produces mesons via ]electron
The electron (, or in nuclear reactions) is a subatomic particle with a negative one elementary charge, elementary electric charge. It is a fundamental particle that comprises the ordinary matter that makes up the universe, along with up qua ...
-positron
The positron or antielectron is the particle with an electric charge of +1''elementary charge, e'', a Spin (physics), spin of 1/2 (the same as the electron), and the same Electron rest mass, mass as an electron. It is the antiparticle (antimatt ...
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
: ''This list is of all known and predicted scalar, pseudoscalar and vector mesons. See list of particles for a more detailed list of particles found in particle physics.''
This article contains a list of mesons, unstable subatomic particles ...
* List of particles
This is a list of known and hypothesized microscopic particles in particle physics, condensed matter physics and cosmology.
Standard Model elementary particles
Elementary particles are particles with no measurable internal structure; that is, ...
* Quark model
In particle physics, the quark model is a classification scheme for hadrons in terms of their valence quarks—the quarks and antiquarks that give rise to the quantum numbers of the hadrons. The quark model underlies "flavor SU(3)", or the Eig ...
References
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Mesons
Onia
Strange quark
Subatomic particles with spin 1