Omega baryon

File:Omega Baryon.svg

Bubble chamber trace of the first observed Ω baryon event at Brookhaven National Laboratory, adapted from original tracing. The tracks of neutral particles (dashed lines) are not visible in the bubble chamber. The collision of a K⁻ meson with a proton creates an Ω⁻, a K⁰ and a K⁺. The Ω⁻ decays into a π⁻ and a Ξ⁰, which in turn decays into a Λ⁰ and a π⁰. The Λ⁰ decays into a proton and a π⁻. The π⁰, invisible due to its short lifetime, decays into two photons (γ), which in turn each create an electron-positron pair.

Omega baryons (often called simply omega particles) are a family of subatomic hadrons which are represented by the symbol Template:SubatomicParticle and are either charge neutral or have a +2, +1 or −1 elementary charge. Additionally, they contain no up or down quarks.<ref name=PDGnaming>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Omega baryons containing top quarks are also not expected to be observed. This is because the Standard Model predicts the mean lifetime of top quarks to be roughly Template:Val,<ref name=Quadt> Template:Cite journal</ref> which is about a twentieth of the timescale necessary for the strong interactions required for hadronization, the process by which hadrons form from quarks and gluons.

The first omega baryon was the Template:SubatomicParticle, it was made of three strange quarks, and was discovered in 1964.<ref> Template:Cite journal</ref> The discovery was a great triumph in the study of quarks, since it was found only after its existence, mass, and decay products had been predicted in 1961 by the American physicist Murray Gell-Mann and, independently, by the Israeli physicist Yuval Ne'eman. Besides the Template:SubatomicParticle, a charmed omega particle (Template:SubatomicParticle) was discovered in 1985, in which a strange quark is replaced by a charm quark. The Template:SubatomicParticle decays only via the weak interaction and has therefore a relatively long lifetime.<ref> {{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Spin (J) and parity (P) values for unobserved baryons are predicted by the quark model.<ref>Template:Cite journal</ref>

Since omega baryons do not have any up or down quarks, they all have isospin 0.

The naming convention of baryons has become such that those with no light (i.e. up or down) valence quarks are called omega baryons. By default, the quarks are strange quarks, but those with one or more the strange quarks replaced by charm or bottom quarks have a subscript c or b, respectively.

Omega baryons

File:Quark structure omega.svg

Quark structure of omega baryon (Template:SubatomicParticle)

Omega

Particle	Symbol	Quark content	Rest mass (MeV/c2)	JP	Q (e)	S	C	Template:Nowrap	Mean lifetime (s)	Decays to
citation	CitationClass=web }}</ref>	Template:SubatomicParticle	Template:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticle	Template:Val	Template:Sfrac+	−1	−3	0	0	Template:Val	Template:Nowrap or Template:Nowrap or Template:Nowrap
citation	CitationClass=web }}</ref>	Template:SubatomicParticle	Template:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticle	Template:Val	Template:Sfrac+	0	−2	+1	0	Template:Val	See Template:SubatomicParticle Decay Modes
Bottom omega<ref name="CDF"/>	Template:SubatomicParticle	Template:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticle	Template:Val	Template:Sfrac+	−1	−2	0	−1	Template:Val	Template:Nowrap (seen)
Double charmed omega†	Template:SubatomicParticle	Template:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticle		Template:Sfrac+	+1	−1	+2	0
Charmed bottom omega†	Template:SubatomicParticle	Template:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticle		Template:Sfrac+	0	−1	+1	−1
Double bottom omega†	Template:SubatomicParticle	Template:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticle		Template:Sfrac+	−1	−1	0	−2
Triple charmed omega†	Template:SubatomicParticle	Template:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticle		Template:Sfrac+	+2	0	+3	0
Double charmed bottom omega†	Template:SubatomicParticle	Template:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticle		Template:Sfrac+	+1	0	+2	−1
Charmed double bottom omega†	Template:SubatomicParticle	Template:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticle		Template:Sfrac+	0	0	+1	−2
Triple bottom omega†	Template:SubatomicParticle	Template:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticle		Template:Sfrac+	−1	0	0	−3

† Particle (or quantity, i.e. spin) has neither been observed nor indicated.

Recent discoveries

The Template:SubatomicParticle particle is a "doubly strange" baryon containing two strange quarks and a bottom quark. A discovery of this particle was first claimed in September 2008 by physicists working on the DØ experiment at the Tevatron facility of the Fermi National Accelerator Laboratory.<ref> {{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref> Template:Cite journal</ref> However, the reported mass of Template:Val was significantly higher than expected in the quark model. The apparent discrepancy from the Standard Model has since been dubbed the "Template:SubatomicParticle puzzle". In May 2009, the CDF collaboration made public their results on the search for the Template:SubatomicParticle based on analysis of a data sample roughly four times the size of the one used by the DØ experiment.<ref name=CDF> Template:Cite journal</ref> CDF measured the mass to be Template:Val, which was in excellent agreement with the Standard Model prediction. No signal has been observed at the DØ reported value. The two results differ by Template:Val, which is equivalent to 6.2 standard deviations and are therefore inconsistent. Excellent agreement between the CDF measured mass and theoretical expectations is a strong indication that the particle discovered by CDF is indeed the Template:SubatomicParticle. In February 2013 the LHCb collaboration published a measurement of the Template:SubatomicParticle mass that is consistent with, but more precise than, the CDF result.<ref name=LHCb>Template:Cite journal</ref>

In March 2017, the LHCb collaboration announced the observation of five new narrow Template:SubatomicParticle states decaying to Template:SubatomicParticleTemplate:SubatomicParticle, where the Template:SubatomicParticle was reconstructed in the decay mode Template:SubatomicParticleTemplate:SubatomicParticleTemplate:SubatomicParticle.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref> The states are named Template:SubatomicParticle(3000)⁰, Template:SubatomicParticle(3050)⁰, Template:SubatomicParticle(3066)⁰, Template:SubatomicParticle(3090)⁰ and Template:SubatomicParticle(3119)⁰. Their masses and widths were reported, but their quantum numbers could not be determined due to the large background present in the sample.

See also

• Delta baryon
• Hyperon
• Lambda baryon
• List of mesons
• List of particles
• Nucleon
• Physics portal
• Sigma baryon
• Timeline of particle discoveries
• Xi baryon

External links

• Picture of the first event containing the Template:SubatomicParticle, which happens to contain the complete decay chain of the Template:SubatomicParticle.
• Science Daily – Discovery of the Template:SubatomicParticle
• Strangeness Minus Three – BBC Horizon 1964