Omega baryon

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

The Omega baryons are a family of subatomic hadron particles that are represented by the symbol Ω and are either neutral or have a +2, +1 or −1 elementary charge. They are baryons containing no up or down quarks.[1] Omega baryons containing top quarks are not expected to be observed. This is because the Standard Model predicts the mean lifetime of top quarks to be roughly 5×10−25 s,[2] which is about a twentieth of the timescale for strong interactions, and therefore that they do 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 in 1962[clarification needed] by the American physicist Murray Gell-Mann and, independently, by the Israeli physicist 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[edit]

Omega
Particle Symbol Quark
content
Rest mass
(MeV/c2)
JP Q
(e)
S C B′ Mean lifetime
(s)
Decays to
Omega[6] Ω sss 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
ssc 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
ssb 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
scc 1/2+ +1 −1 +2 0
Charmed bottom Omega† Ω0
cb
scb 1/2+ 0 −1 −1 −1
Double bottom Omega† Ω
bb
sbb 1/2+ −1 −1 0 −2
Triple charmed Omega† Ω++
ccc
ccc 3/2+ +2 0 +3 0
Double charmed bottom Omega† Ω+
ccb
ccb 1/2+ +1 0 +2 −1
Charmed double bottom Omega† Ω0
cbb
cbb 1/2+ 0 0 +1 −2
Triple bottom Omega† Ω
bbb
bbb 3/2+ −1 0 0 −3

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

Recent discoveries[edit]

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 experiment at the Tevatron facility of the Fermi National Accelerator Laboratory.[9][10] However, the reported mass, 6165±16 MeV/c2, was significantly higher than expected in the quark model. The apparent discrepancy from the Standard Model has since been dubbed the "Ω
b
puzzle". In May 2009, the CDF collaboration made public their results on the search for the Ω
b
based on analysis of a data sample roughly four times the size of the one used by the DØ experiment.[8] CDF measured the mass to be 6054.4±6.8 MeV/c2, 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 111±18 MeV/c2, 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 Ω
b
.

See also[edit]

References[edit]

  1. ^ Particle Data Group. "2010 Review of Particle Physics – Naming scheme for hadrons" (PDF). Retrieved 2011-12-26. 
  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 Minus Three" (PDF). Physical Review Letters. 12 (8): 204. Bibcode:1964PhRvL..12..204B. doi:10.1103/PhysRevLett.12.204. 
  4. ^ R. Nave. "The Omega baryon". HyperPhysics. Retrieved 2009-11-26. 
  5. ^ J. G. Körner; M. Krämer & D. Pirjol (1994). "Heavy Baryons". Progress in Particle and Nuclear Physics. 33: 787–868. arXiv:hep-ph/9406359free to read. Bibcode:1994PrPNP..33..787K. doi:10.1016/0146-6410(94)90053-1. 
  6. ^ Particle Data Group. "2006 Review of Particle Physics – Ω" (PDF). Retrieved 2008-04-20. 
  7. ^ Particle Data Group. "2006 Review of Particle Physics – Ω0
    c
    "
    (PDF). Retrieved 2008-04-20.
     
  8. ^ 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:0905.3123free to read. Bibcode:2009PhRvD..80g2003A. doi:10.1103/PhysRevD.80.072003.
     
  9. ^ "Fermilab physicists discover "doubly strange" particle". Fermilab. 3 September 2008. Retrieved 2008-09-04. 
  10. ^ V. Abazov et al. (DØ Collaboration) (2008). "Observation of the doubly strange b baryon Ω
    b
    ". Physical Review Letters. 101 (23): 232002. arXiv:0808.4142free to read. Bibcode:2008PhRvL.101w2002A. doi:10.1103/PhysRevLett.101.232002.
     

External links[edit]