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 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 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 S C B' Mean lifetime
s
Decays to
Omega[6] Ω sss 1672.45±0.29 32+ −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 12+ 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 12+ −1 −2 0 −1 (1.13±0.53)×10−12 Ω + J/ψ (seen)
Double charmed Omega† Ω+
cc
scc 12+ +1 −1 +2 0
Charmed bottom Omega† Ω0
cb
scb 12+ 0 −1 −1 −1
Double bottom Omega† Ω
bb
sbb 12+ −1 −1 0 −2
Triple charmed Omega† Ω++
ccc
ccc 32+ +2 0 +3 0
Double charmed bottom Omega† Ω+
ccb
ccb 12+ +1 0 +2 −1
Charmed double bottom Omega† Ω0
cbb
cbb 12+ 0 0 +1 −2
Triple bottom Omega† Ω
bbb
bbb 32+ −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 Tevatron facility of 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
.

See also[edit]

References[edit]

  1. ^ Particle Data Group. "2010 Review of Particle Physics – Naming scheme for hadrons". 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". 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, 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. 
  6. ^ Particle Data Group. "2006 Review of Particle Physics – Ω". Retrieved 2008-04-20. 
  7. ^ Particle Data Group. "2006 Review of Particle Physics – Ω0
    c
    "
    . 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:0905.3123. 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:0808.4142. Bibcode:2008PhRvL.101w2002A. doi:10.1103/PhysRevLett.101.232002.
     

External links[edit]