View source for Vector meson

{{Short description|Meson with total spin 1 and odd parity}}
{{More citations needed|date=June 2021}}
[[File:Noneto mesônico de spin 1.png|thumb|The vector mesons consisting of light quarks form a [[Quark model#Mesons|nonet]].]]

In [[high energy physics]], a '''vector meson''' is a [[meson]] with [[total angular momentum quantum number|total spin]] 1 and odd [[parity (physics)|parity]] (usually noted as {{nowrap|''J<sup>P</sup>'' {{=}} 1<sup>&minus;</sup>}}). Vector mesons have been seen in experiments since the 1960s, and are well known for their [[Spectroscopy|spectroscopic]] pattern of masses.<ref>{{cite web|url=https://inis.iaea.org/collection/NCLCollectionStore/_Public/28/026/28026670.pdf|title=An Introduction to the Vector Meson|first=F.|last=Nichitiu|date=November 2, 1995|access-date=June 1, 2021}}</ref>

The vector mesons contrast with the [[pseudovector meson]]s, which also have a total spin 1 but instead have even parity. The vector and pseudovector mesons are also dissimilar in that the spectroscopy of vector mesons tends to show nearly pure states of constituent [[quark]] [[Flavour (particle physics)|flavors]], whereas pseudovector mesons and [[scalar meson]]s tend to be expressed as composites of mixed states.

==Uniquely pure flavor states==
Since the development of the [[quark model]] by [[Murray Gell-Mann]] (and also independently by [[George Zweig]]),<ref>{{cite journal |last=Gell-Mann |first=M. |author-link=Murray Gell-Mann |date=4 January 1964
 |title=A Schematic Model of Baryons and Mesons |journal=[[Physics Letters]]
 |doi=10.1016/S0031-9163(64)92001-3 |bibcode = 1964PhL.....8..214G |volume=8 |number=3 |pages=214–215}}</ref><ref>{{cite report |last=Zweig |first=G. |author-link=George Zweig |date=17 January 1964 |title=An SU(3) Model for Strong Interaction Symmetry and its Breaking  |id=CERN Report No.8182/TH.401 |url=https://cds.cern.ch/record/352337/files/CERN-TH-401.pdf}}</ref><ref>{{cite report|last=Zweig |first=G. |author-link=George Zweig |year=1964 |title=An SU(3) Model for Strong Interaction Symmetry and its Breaking: II |id=CERN Report No.8419/TH.412 |url=https://cds.cern.ch/record/570209/files/CERN-TH-412.pdf}}</ref> the vector mesons have demonstrated the spectroscopy of pure states. The fact that the {{nowrap|[[Isospin|{{mvar|I}}]] {{=}} 1}} [[rho meson]] (&rho;) and {{nowrap|{{mvar|I}} {{=}} 0}} [[omega meson]] (&omega;) have nearly equal mass centered on 770–{{val|780|ul=MeV/c2}}, while the [[phi meson]] (&phi;) has a higher mass around {{val|1020|u=MeV/c2}}, indicates that the light-quark vector mesons appear in nearly pure states, with the &phi; meson having a nearly 100&nbsp;percent amplitude of hidden [[strangeness]].

These nearly pure states characteristic of the vector mesons are not at all evident in the [[pseudoscalar meson]] or scalar meson [[multiplets]], and may be only slightly realized among the [[tensor meson]] and pseudovector meson multiplets. This fact makes the vector mesons an excellent probe of the quark flavor content of other types of mesons, measured through the respective [[decay rate]]s of non-vector mesons into the different types of vector mesons. Such experiments are very revealing for theorists who seek to determine the flavor content of mixed state mesons.

==Backbone of meson spectroscopy==
At higher masses, the vector mesons include [[charm quark|charm]] and [[bottom quark]]s in their structure. In this realm, the [[radiative process]]es tend to stand out, with heavy tensor and scalar mesons decaying dominantly into vector mesons by [[photon emission]]. Pseudovector mesons transition by a similar process into pseudoscalar mesons. Because much of the spectrum of heavy mesons is tied by radiative processes to the vector mesons, one may think of vector mesons as forming a sort of backbone to the [[Meson spectroscopy|spectroscopy of mesons]] in general. 

Some vector mesons can, compared to other mesons, be measured to a very high precision. This stems from the fact that they have the same quantum numbers as the photon, {{nowrap|''J<sup>PC</sup>''  {{=}} 1<sup>−−</sup>}}, where ''J'' = [[angular momentum quantum number]], ''P'' = [[Parity (physics)|parity]], ''C'' = [[C parity]]. Therefore they appear in electron-positron collisions in the process <math>e^- e^+ \to \gamma \to q\bar q</math>, which provides experimentally a clear signal compared to other measurements, which have to use hadronic processes. Vector mesons play a huge role in the study of the strong hadronic force.

==List of vector mesons==
* [[rho meson|&rho; meson]]
* [[omega meson|&omega; meson]]
* [[phi meson|&phi; meson]]
* [[Kaon|K*(892) meson]]
* [[D meson|D* meson]]
* [[J/Psi meson|{{SubatomicParticle|J/Psi}} meson]]
* [[Upsilon meson|{{SubatomicParticle|Upsilon}} meson]]

===Hypothetical===
* [[Theta meson|&theta; meson]]

==See also==
* [[List of mesons]]
* [[Vector meson dominance]]
* [[Vector boson]]

==References==
{{reflist}}

{{DEFAULTSORT:Vector Meson}}
[[Category:Mesons]]
[[Category:Subatomic particles with spin 1]]
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