Omega meson

Not to be confused with Omega baryon.

The omega meson (ω) is a flavourless meson formed from a superposition of an up quark–antiquark and a down quark–antiquark pair. It is part of the vector meson nonet^[4][5] and mediates the nuclear force along with pions and rho mesons.

Omega meson

Composition	${\textstyle \approx {\frac {u{\bar {u}}+d{\bar {d}}}{\sqrt {2}}}}$
Statistics	Bosonic
Family	Mesons
Interactions	Strong, weak, electromagnetic, gravity
Symbol	ω
Antiparticle	Self
Theorized	Yoichiro Nambu[1] (1957)
Discovered	Lawrence Berkeley National Laboratory (1961)[2][3]
Types	1
Mass	782.66±0.13 MeV/c2
Mean lifetime	(7.58±0.11)×10−23 s
Decays into	π+ +π0 +π− or π0 +γ
Electric charge	0 e
Spin	1
Isospin	0
Hypercharge	0
Parity	−1
C parity	−1

Properties

The most common decay mode for the ω meson is π⁺
π⁰
π⁻
at 89.2%±0.7%, followed by π⁰
γ at 8.34%±0.26%.^[6]

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)
Omega meson[6]	ω(782)	Self	${\textstyle {\frac {u{\bar {u}}+d{\bar {d}}}{\sqrt {2}}}}$	782.66 ± 0.13	0−	1−−	0	0	0	(7.58±0.11)×10−23 s	π+ +π0 +π−  or π0 +γ

The quark composition of the ω meson can be thought of as a mix between uu, dd and ss states, but it is very nearly a pure symmetric uu–dd state. This can be shown by deconstructing the wave function of the ω into its component parts. We see that the ω and ϕ mesons are mixtures of the SU(3) wave functions as follows.^[7]

${\displaystyle \omega =\psi _{8}\sin \theta +\psi _{1}\cos \theta }$,

${\displaystyle \phi =\psi _{8}\cos \theta -\psi _{1}\sin \theta }$,

where

${\displaystyle \theta }$ is the nonet mixing angle,

${\displaystyle \psi _{1}={\frac {u{\overline {u}}+d{\overline {d}}+s{\overline {s}}}{\sqrt {3}}}}$ and

${\displaystyle \psi _{8}={\frac {u{\overline {u}}+d{\overline {d}}-2s{\overline {s}}}{\sqrt {6}}}}$.

The mixing angle at which the components decouple completely can be calculated to be ${\textstyle \arctan {\frac {1}{\sqrt {2}}}\approx 35.3^{\circ }}$, which almost corresponds to the actual value calculated from the masses of 35°. Therefore, the ω meson is nearly a pure symmetric uu–dd state.

See also

• List of mesons
• Quark model
• Vector meson