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The Omega baryons are a family of subatomic hadron particles which have the symbols
Ω
and have a +2, +1 or −1 elementary charge or are neutral. They are baryons containing no up or down quarks.^[1] Omega baryons containing top quarks are not expected to be observed as the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10⁻²⁵ s.^[2] This is about 20 times shorter than the timescale for strong interactions, and therefore it does not form hadrons.

The first Omega baryon discovered was the
Ω⁻
, made of three strange quarks, in 1964.^[3] The discovery was a great triumph in the study of quark processes, since it was found only after its existence, mass, and decay products had been predicted by American physicist Murray Gell-Mann in 1962 and independently by Yuval Ne'eman. Besides the
Ω⁻
, a charmed Omega particle (
Ω⁰
_c) was discovered, in which a strange quark is replaced by a charm quark. The
Ω⁻
decays only via the weak interaction and has therefore a relatively long lifetime.^[4] Spin (J) and parity (P) values for unobserved baryons are predicted by the quark model.^[5]

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

Omega baryons

Omega
Particle	Symbol	Quark content	Rest mass MeV/c²	J^P	Q	S	C	B'	Mean lifetime s	Decays to
Omega^[6]	Ω⁻	s s s	1672.45±0.29	3⁄2⁺	−1	−3	0	0	(8.21±0.11)×10⁻¹¹	Λ⁰ + K⁻ or Ξ⁰ + π⁻ or Ξ⁻ + π⁰
Charmed Omega^[7]	Ω⁰ _c	s s c	2697.5±2.6	1⁄2⁺	0	−2	+1	0	(6.9±1.2)×10⁻¹⁴	See Ω⁰ _c Decay Modes
Bottom Omega^[8]	Ω⁻ _b	s s b	6054.4±6.8	1⁄2⁺	−1	−2	0	−1	(1.13±0.53)×10⁻¹²	Ω⁻ + J/ψ (seen)
Double charmed Omega†	Ω⁺ _cc	s c c		1⁄2⁺	+1	−1	+2	0
Charmed bottom Omega†	Ω⁰ _cb	s c b		1⁄2⁺	0	−1	−1	−1
Double bottom Omega†	Ω⁻ _bb	s b b		1⁄2⁺	−1	−1	0	−2
Triple charmed Omega†	Ω⁺⁺ _ccc	c c c		3⁄2⁺	+2	0	+3	0
Double charmed bottom Omega†	Ω⁺ _ccb	c c b		1⁄2⁺	+1	0	+2	−1
Charmed double bottom Omega†	Ω⁰ _cbb	c b b		1⁄2⁺	0	0	+1	−2
Triple bottom Omega†	Ω⁻ _bbb	b b b		3⁄2⁺	−1	0	0	−3

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

Recent discoveries

The
Ω⁻
_b 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 DZero experiment at the Fermi National Accelerator Laboratory.^[9]^[10] However, the reported mass, 6165±16 MeV/c², was significantly higher than expected in quark model. The apparent discrepancy from Standard Model has since been dubbed "
Ω
_b puzzle". In May 2009 the CDF collaboration made public their results on search for
Ω⁻
_b based on analysis of data sample roughly four times larger than the one used by DØ experiment.^[8] CDF measured mass to be 6054.4±6.8 MeV/c² in excellent agreement with Standard Model prediction. No signal has been observed at DØ reported value. The two results differ by 111±18 MeV/c² or by 6.2 standard deviations and therefore are inconsistent. Excellent agreement between CDF measured mass and theoretical expectations is a strong indication that the particle discovered by CDF is indeed the
Ω⁻
_b.

References

^ Particle Data Group. "2010 Review of Particle Physics – Naming scheme for hadrons" (PDF). Retrieved 26 December 2011.
^ A. Quadt (2006). "Top quark physics at hadron colliders". European Physical Journal C. 48 (3): 835–1000. Bibcode:2006EPJC...48..835Q. doi:10.1140/epjc/s2006-02631-6.
^ V. E. Barnes; et al. (1964). "Observation of a Hyperon with Strangeness Number Three" (PDF). Physical Review Letters. 12 (8): 204. Bibcode:1964PhRvL..12..204B. doi:10.1103/PhysRevLett.12.204. {{cite journal}}: Explicit use of et al. in: |author= (help)
^ R. Nave. "The Omega baryon". HyperPhysics. Retrieved 26 November 2009.
^ J. G. Körner, M. Krämer, and D. Pirjol (1994). "Heavy Baryons". Progress in Particle and Nuclear Physics. 33: 787–868. arXiv:hep-ph/9406359. Bibcode:1994PrPNP..33..787K. doi:10.1016/0146-6410(94)90053-1.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^ Particle Data Group. "2006 Review of Particle Physics –
Ω⁻
" (PDF). Retrieved 20 April 2008.
^ Particle Data Group. "2006 Review of Particle Physics –
Ω⁰
_c" (PDF). Retrieved 20 April 2008.
^ ^a ^b T. Aaltonen et al. (CDF Collaboration) (2009). "Observation of the
Ω⁻
_b and Measurement of the Properties of the
Ξ⁻
_b and
Ω⁻
_b". Physical Review D. 80 (7). arXiv:0905.3123. Bibcode:2009PhRvD..80g2003A. doi:10.1103/PhysRevD.80.072003.
^ "Fermilab physicists discover "doubly strange" particle". Fermilab. 3 September 2008. Retrieved 4 September 2008.
^ V. Abazov et al. (DØ Collaboration) (2008). "Observation of the doubly strange b baryon
Ω⁻
_b". Physical Review Letters. 101 (23): 232002. arXiv:0808.4142. Bibcode:2008PhRvL.101w2002A. doi:10.1103/PhysRevLett.101.232002.

External links

[PDGnaming-1] Particle Data Group. "2010 Review of Particle Physics – Naming scheme for hadrons" (PDF). Retrieved 26 December 2011.

[Quadt-2] A. Quadt (2006). "Top quark physics at hadron colliders". European Physical Journal C. 48 (3): 835–1000. Bibcode:2006EPJC...48..835Q. doi:10.1140/epjc/s2006-02631-6.

[3] V. E. Barnes; et al. (1964). "Observation of a Hyperon with Strangeness Number Three" (PDF). Physical Review Letters. 12 (8): 204. Bibcode:1964PhRvL..12..204B. doi:10.1103/PhysRevLett.12.204. {{cite journal}}: Explicit use of et al. in: |author= (help)

[4] R. Nave. "The Omega baryon". HyperPhysics. Retrieved 26 November 2009.

[5] J. G. Körner, M. Krämer, and D. Pirjol (1994). "Heavy Baryons". Progress in Particle and Nuclear Physics. 33: 787–868. arXiv:hep-ph/9406359. Bibcode:1994PrPNP..33..787K. doi:10.1016/0146-6410(94)90053-1.{{cite journal}}: CS1 maint: multiple names: authors list (link)

[PDGOmega--6] Particle Data Group. "2006 Review of Particle Physics –
Ω⁻
" (PDF). Retrieved 20 April 2008.

[PDGCharmedOmega0-7] Particle Data Group. "2006 Review of Particle Physics –
Ω⁰
_c" (PDF). Retrieved 20 April 2008.

[CDF-8] T. Aaltonen et al. (CDF Collaboration) (2009). "Observation of the
Ω⁻
_b and Measurement of the Properties of the
Ξ⁻
_b and
Ω⁻
_b". Physical Review D. 80 (7). arXiv:0905.3123. Bibcode:2009PhRvD..80g2003A. doi:10.1103/PhysRevD.80.072003.

[9] "Fermilab physicists discover "doubly strange" particle". Fermilab. 3 September 2008. Retrieved 4 September 2008.

[10] V. Abazov et al. (DØ Collaboration) (2008). "Observation of the doubly strange b baryon
Ω⁻
_b". Physical Review Letters. 101 (23): 232002. arXiv:0808.4142. Bibcode:2008PhRvL.101w2002A. doi:10.1103/PhysRevLett.101.232002.

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@@ Line 214: / Line 214: @@
  |bibcode=2009PhRvD..80g2003A
  |doi=10.1103/PhysRevD.80.072003
-}}</ref> [[Collider Detector at Fermilab|CDF]] measured mass to be {{val|6054.4|6.8|u=MeV/c2}} in excellent agreement with Standard Model prediction. No signal has been observed at DZero reported value. The two results differ by {{val|111|18|u=MeV/c2}} or by 6.2 standard deviations and therefore are inconsistent. Excellent agreement between CDF measured mass and theoretical expectations is a strong indication that the particle discovered by CDF is indeed the {{SubatomicParticle|Bottom Omega-}}.
+}}</ref> [[Collider Detector at Fermilab|CDF]] measured mass to be {{val|6054.4|6.8|u=MeV/c2}} in excellent agreement with Standard Model prediction. No signal has been observed at DØ reported value. The two results differ by {{val|111|18|u=MeV/c2}} or by 6.2 standard deviations and therefore are inconsistent. Excellent agreement between CDF measured mass and theoretical expectations is a strong indication that the particle discovered by CDF is indeed the {{SubatomicParticle|Bottom Omega-}}.
 ==See also==