View source for Phi meson

{{Distinguish|text=the &Phi;<sup>−−</sup>, formerly thought to be a [[pentaquark]]}}
[[File:Quark structure phi meson.svg|thumb|Quark structure of the phi meson, is a vector meson formed of a strange quark and a strange antiquark.]]
{{Infobox particle
| name = Phi meson
| image = OZI rule - Feynmann diagram.svg{{!}}class=skin-invert-image
| caption = Feynman diagram of the most common {{Subatomic particle|Phi meson}} meson decay
| num_types = 1
| composition = {{Subatomic particle|phi meson0}}: {{Subatomic particle|strange quark}}{{Subatomic particle|strange antiquark}}
| statistics = [[Bosonic]]
| group = [[Meson]]s
| interaction = [[Strong interaction|Strong]], [[Weak interaction|Weak]], [[Gravity]], [[Electromagnetism]]
| antiparticle = Self
| status = 
| theorized = {{harvp|Sakurai|1962}}
| discovered = {{harvp|Connolly|Hart|Lai|London|Moneti|1963}}
| symbol = {{Subatomic particle|phi meson}}, {{Subatomic particle|phi meson0}}
| mass = {{val|1019.461|0.020|ul=MeV/c2}}
| mean_lifetime = {{val|1.55|0.01|e=-22|u=s}}
| decay_particle = {{plainlist|
*{{Subatomic particle|link=yes|Kaon+}} + {{Subatomic particle|link=yes|Kaon-}}
*{{Subatomic particle|link=yes|K-short0}} + {{Subatomic particle|link=yes|K-long0}}
*{{Subatomic particle|link=yes|rho}} + {{Subatomic particle|link=yes|pion}}
*{{Subatomic particle|link=yes|pion+}} + {{Subatomic particle|link=yes|pion0}} + {{Subatomic particle|link=yes|pion-}}}}
| electric_charge = 0
| spin = 1
| strangeness = 
| charm = 
| bottomness = 
| topness = 
| isospin = 0
| hypercharge = 0
| parity = −1
| c_parity = −1
}}

In [[particle physics]], the '''phi meson''' or '''{{Subatomic particle|Phi meson}} meson''' is a [[vector meson|vector]] [[meson]] formed of a [[strange quark|strange]] [[quark]] and a [[antistrange quark|strange]] [[antiparticle|antiquark]]. It was the {{Subatomic particle|Phi meson}} meson's unexpected propensity to decay into {{SubatomicParticle|link=yes|Kaon0}} and {{SubatomicParticle|link=yes|Antikaon0}} that led to the discovery of the [[OZI rule]]. It has a mass of {{val|1019.461|0.020|ul=MeV/c2}} and a mean lifetime of {{nobr| 1.55±0.01 × {{10^|−22}} [[second (unit)|s]] .}}

==Properties==
The most common decay modes of the {{Subatomic particle|Phi meson}} meson are {{Subatomic particle|link=yes|Kaon+}}{{Subatomic particle|link=yes|Kaon-}} at {{val|48.9|0.5|u=%}}, {{Subatomic particle|link=yes|K-short0}}+{{Subatomic particle|link=yes|K-long0}} at {{val|34.2|0.4|u=%}}, and various indistinguishable mixed combinations of [[rho meson]]s and [[pions]] at {{val|15.3|0.3|u=%}}.<ref name=Nakamura>{{cite web |last1=Nakamura |first1=K. |collaboration=[[Particle Data Group]] |year=2010 |department=Particle listings |title={{Subatomic particle|Phi meson}} |publisher=[[Lawrence Berkeley Laboratory]] |place=Lawrence, CA |url=http://pdg.lbl.gov/2010/listings/rpp2010-list-phi-1020.pdf |access-date=5 May 2017}}</ref> In all cases, it decays via the [[Strong interaction|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 {{Subatomic particle|Phi meson}} meson can be thought of as a mix between {{Subatomic particle|strange quark}}{{Subatomic particle|strange antiquark}}, {{Subatomic particle|link=yes|up quark}}{{Subatomic particle|link=yes|up antiquark}}, and {{Subatomic particle|link=yes|down quark}}{{Subatomic particle|link=yes|down antiquark}} states, but it is very nearly a pure {{Subatomic particle|strange quark}}{{Subatomic particle|strange antiquark}} state.<ref name="Nakamura 2">{{cite report |last1=Nakamura |first1=K. |collaboration=[[Particle Data Group]] |year=2011 |title=14. Quark Model |publisher=[[Lawrence Berkeley Laboratory]] |place=Lawrence, CA |url=http://pdg.lbl.gov/2011/reviews/rpp2011-rev-quark-model.pdf |access-date=3 June 2021 }}</ref> This can be shown by deconstructing the [[wave function]] of the {{Subatomic particle|Phi meson}} into its component parts. We see that the {{Subatomic particle|Phi meson}} and {{Subatomic particle|Omega meson}} mesons are mixtures of the [[SU(3)]] wave functions as follows.
: <math>\phi = \psi_8\ \cos\theta\ -\ \psi_1\ \sin\theta</math>,
: <math>\omega = \psi_8\ \sin\theta\ +\ \psi_1\ \cos\theta</math>,

where
: <math>\theta</math> is the nonet mixing angle,
: <math>\psi_8 = \frac{\ u\overline{u} + d\overline{d} - 2s\overline{s}\ }{ \sqrt{6\ } }~</math> and
: <math>\psi_1 = \frac{\ u\overline{u} + d\overline{d} + s\overline{s}\ }{ \sqrt{3\ } } ~.</math>

The mixing angle at which the components decouple completely can be calculated to be <math display="inline">\ \arctan\frac{ 1 }{ \sqrt{2\ } } \approx 35.3^\circ ~.</math> The mixing angle of the {{Subatomic particle|Phi meson}} and {{Subatomic particle|Omega meson}} states is calculated from the masses of each state to be about 35˚, which is very close to maximum decoupling. Therefore, the {{Subatomic particle|Phi meson}} meson is nearly a pure {{Subatomic particle|strange quark}}{{Subatomic particle|strange antiquark}} state.<ref name="Nakamura 2"/>

==History==
The existence of the {{Subatomic particle|Phi meson}} meson was first proposed by the Japanese American particle physicist, [[J. J. Sakurai]], in 1962 as a resonance state between the {{SubatomicParticle|link=yes|Kaon0}} and the {{SubatomicParticle|link=yes|Antikaon0}}.<ref name="Sakurai">{{cite journal |last1=Sakurai |first1=J.J. |date=December 1962 |title=Possible existence of a {{nobr| {{math|T {{=}} 0}} }} vector meson at 1020&nbsp;MeV |journal=[[Physical Review Letters]] |volume=9 |issue=11 |pages=472–475 |doi=10.1103/PhysRevLett.9.472 |bibcode=1962PhRvL...9..472S |url=https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.9.472 |access-date=5 May 2017 }}</ref> It was discovered later by {{harvp|Connolly|Hart|Lai|London|Moneti|1963}} in a 20&nbsp;inch hydrogen bubble chamber at the [[Alternating Gradient Synchrotron|Alternating Gradient Synchrotron (AGS)]] in [[Brookhaven National Laboratory]] in [[Upton, New York|Uptown, NY]] while they were studying {{SubatomicParticle|link=yes|Kaon-}}{{Subatomic particle|link=yes|Proton+}} collisions at approximately 2.23&nbsp;GeV/{{mvar|c}}.<ref name="APS: Discovery">{{cite journal |last1=Connolly |first1=P.L. |last2=Hart |first2=E.L. |last3=Lai |first3=K.W. |last4=London |first4=G. |last5=Moneti |first5=G.C. |last6=Rau|first6=R. R.|last7=Samios|first7=N.P. |last8=Skillicorn |first8=I.O. |last9=Yamamoto |first9=S.S. |last10=Goldberg|first10=M. |last11=Gundzik |first11=M. |last12=Leitner |first12=J. |last13=Lichtman |first13=S. |display-authors=6 |date=15 April 1963 |title=Existence and properties of the {{Subatomic particle|Phi meson}} meson |journal=[[Physical Review Letters]] |volume=10 |issue=8 |pages=371–376 |doi=10.1103/PhysRevLett.10.371 |bibcode=1963PhRvL..10..371C|osti=12491318 |url=https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.10.371 |access-date=5 May 2017 }}</ref><ref name=K>{{cite press release |title='K' for KLOE ... and 'Z' for Zweig |date=30 August 1999 |series=[[CERN Courier]] |url=http://cerncourier.com/cws/article/cern/28072 |via=cerncourier.com |access-date=6 May 2017}}</ref> In essence, the reaction involved a beam of {{SubatomicParticle|Kaon-}}s being accelerated to high energies to collide with protons.

The {{Subatomic particle|Phi meson}} meson has several possible decay modes. The most energetically favored mode involves the {{Subatomic particle|Phi meson}} meson decaying into three [[pions]], which is what would naïvely be expected. However, we instead observe that it decays most frequently into two [[kaons]].<ref name=Griffiths>{{cite book |last=Griffiths |first=David |year=2008 |title=Introduction to Elementary Particles |edition=2nd rev. |publisher=Wiley-VCH |location=Weinheim, DE |isbn=978-3-527-40601-2 }}</ref> 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.<ref>{{cite journal |first=S. |last=Okubo |author-link=Susumu Okubo |year=1975 |title={{grey|[no title cited]}} |journal=[[Phys. Lett.]] |volume=5 |orig-year=1963 }}</ref><ref>{{cite report |first=G. |last=Zweig |author-link=George Zweig |year=1964 |title={{grey|[no title cited]}} |series=[[CERN]] Report |id=8419/TH412 }}</ref><ref>{{cite journal |first=J. |last=Iizuka |year=1966 |title={{grey|[no title cited]}} |journal=[[Prog. Theor. Phys. Suppl.]] |volume=37 |issue=21 }}</ref> This rule is now known as the [[OZI rule]] and is also the currently accepted explanation for the unusually long lifetimes of the {{Subatomic particle|link=yes|J/Psi}} and {{Subatomic particle|link=yes|Upsilon}} mesons.<ref name=Griffiths/> Namely, on average they last {{nobr| ~ 7 × {{10^|−21}} [[second (unit)|s]] }} and {{nobr| ~ 1.5 × {{10^|−20}} s }} respectively.<ref name=Griffiths/> This is compared to the normal mean lifetime of a meson decaying via the strong force, which is on the order of {{nobr| {{10^|−23}} s .}}<ref name=Griffiths/>

In 1999, a {{Subatomic particle|Phi meson}} factory named [[DAFNE]] (or DA{{Subatomic particle|Phi meson}}NE since the F stands for "{{Subatomic particle|Phi meson}} Factory") began operation to study the decay of the {{Subatomic particle|Phi meson}} meson in [[Frascati]], [[Italy]].<ref name=K/> It produces {{Subatomic particle|Phi meson}} mesons via [[electron]]-[[positron]] collisions. It has numerous detectors, including the [[KLOE (experiment)|KLOE detector]] which was in operation at the beginning of its operation.

{| class="wikitable"
! class=unsortable|Particle name
! Particle <br>symbol
! Antiparticle <br>symbol
! class=unsortable|Quark<br>content
! [[Rest mass]] ([[electron volt|MeV]]/''[[speed of light|c]]''<sup>2</sup>)
! width="50"|''[[Isospin|I]]<sup>[[G parity|G]]</sup>''
! width="50"|''[[Total angular momentum|J]]<sup>[[Parity (physics)|P]][[C-parity|C]]</sup>''
! width="50"|''[[strangeness|S]]''
! width="50"|''[[charm (quantum number)|C]]''
! width="50"|''[[bottomness|B']]''
! [[Mean lifetime]] ([[second|s]])
! class=unsortable|Commonly decays to<br>
(>5% of decays)
|-
| Phi meson<ref name=PDG2018-phi>{{cite report |last1=Tanabashi |first1=M. |collaboration=[[Particle Data Group]] |year=c. 2019 |department=Particle listings |title={{Subatomic particle|Phi meson}} |publisher=[[Lawrence Berkeley Laboratory]] |place=Lawrence, CA |url=http://pdglive.lbl.gov/Particle.action?node=M004&init=0&home=MXXX005 |access-date=17 Feb 2019 }}</ref>
|align="center"| {{Subatomic particle|Phi meson}}(1020)
|align="center"| Self
|align="center"| {{Subatomic particle|link=yes|Strange quark}}{{Subatomic particle|link=yes|Strange antiquark}}
|align="center"| {{nobr|1,019.461 ± 0.020}}
|align="center"| {{nobr|0<sup>&minus;</sup>}}
|align="center"| {{nobr|1<sup>&minus;&minus;</sup>}}
|align="center"| 0
|align="center"| 0
|align="center"| 0
|align="center"| {{nobr|1.55 ± 0.01 × {{10^|−22}} }}<sup>{{ref|Lifetime2|[f]}}</sup>
|align="center"| {{nobr|{{Subatomic particle|link=yes|Kaon+}} + {{Subatomic particle|link=yes|Kaon-}}   or}}<br> {{nobr|{{Subatomic particle|link=yes|K-short0}} + {{Subatomic particle|link=yes|K-long0}}   or}}<br> {{nobr|({{Subatomic particle|link=yes|rho}} + {{Subatomic particle|link=yes|pion}}) / ({{Subatomic particle|link=yes|pion+}} + {{Subatomic particle|link=yes|pion0}} + {{Subatomic particle|link=yes|pion-}})}}
|-
|}

==See also==
* [[Charmonium]]
* [[List of mesons]]
* [[List of particles]]
* [[Quark model]]

==References==
{{reflist|25em}}

{{Particles}}
{{Authority control}}

[[Category:Mesons]]
[[Category:Onia]]
[[Category:Strange quark]]
[[Category:Subatomic particles with spin 1]]