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|volume=12 |issue=8 |page=p.204
|volume=12 |issue=8 |page=p.204
|year=1964
|year=1964
}}</ref> 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 already been predicted. Besides the {{SubatomicParticle|Omega-}}, a charmed Omega particle ({{SubatomicParticle|Charmed Omega0}}) was discovered, in which a [[strange quark]] is replaced by a [[charm quark]]. The {{SubatomicParticle|Omega-}} decays only via the weak interaction and has therefore a relatively long lifetime.<ref>
}}</ref> 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 [[United States|American]] [[physicist]] [[Murray Gell-Mann]] in 1962. Besides the {{SubatomicParticle|Omega-}}, a charmed Omega particle ({{SubatomicParticle|Charmed Omega0}}) was discovered, in which a [[strange quark]] is replaced by a [[charm quark]]. The {{SubatomicParticle|Omega-}} decays only via the weak interaction and has therefore a relatively long lifetime.<ref>
{{cite web
{{cite web
|author=R. Nave
|author=R. Nave

Revision as of 02:19, 19 March 2010

"Omega particle" redirects here. For the Star Trek particle, see The Omega Directive.
Bubble chamber trace of the first observed Ω baryon event at Brookhaven National Laboratory.

Omega (Ω) baryons are baryons containing neither up nor down quarks. The first Omega discovered was the
Ω−
, made of three strange quarks, in 1964.[1] 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. 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.[2] Spin (J) and parity (P) values for unobserved baryons are predicted by the quark model.[3]

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 		JP Q S C B Mean lifetime
s 		Decays to
Omega[4]
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[5]
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 [6]
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.[7][8] 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 DZero experiment.[9] CDF measured mass to be 6054.4±6.8 MeV/c2 in excellent agreement with Standard Model prediction. No signal has been observed at DZero 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.

See also

References

  1. ^ V.E. Barnes; et al. (1964). "Observation of a Hyperon with Strangeness Number Three" (PDF). Physical Review Letters. 12 (8): p.204. {{cite journal}}: |page= has extra text (help); Explicit use of et al. in: |author= (help)
  2. ^ R. Nave. "The Omega baryon". Retrieved 2009-11-26.
  3. ^ J. G. Körner, M. Krämer, and D. Pirjol (1994). "Heavy Baryons". Progress in Particle and Nuclear Physics. 33: 787–868. doi:10.1016/0146-6410(94)90053-1. arXiv:hep-ph/9406359.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  4. ^ "Particle Data Groups: 2006 Review of Particle Physics - Omega-" (PDF). Retrieved 2008-04-20.
  5. ^ "Particle Data Groups: 2006 Review of Particle Physics - Charmed Omega0" (PDF). Retrieved 2008-04-20.
  6. ^ "Observation of the Omega_b^- and Measurement of the Properties of the Xi_b^- and Omega_b^-". Retrieved 2009-05-19.
  7. ^ "Fermilab physicists discover "doubly strange" particle". Fermilab. 3 September 2008. Retrieved 2008-09-04.
  8. ^ D0 Collaboration; Abazov (2008). "Observation of the doubly strange b baryon Omega_b-, Fermilab-Pub-08/335-E". arXiv:0808.4142 [hep-ex].{{cite arXiv}}: CS1 maint: numeric names: authors list (link)
  9. ^ CDF Collaboration; Aaltonen (2009). "Observation of the
    Ω−
    b     and Measurement of the Properties of the
    Ξ−
    b     and
    Ω−
    b    ". arXiv:0905.3123 [hep-ex].
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