Omega baryon

"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

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 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

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 DØ 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

References

  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, 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−" (PDF). Retrieved 2008-04-20.
  7. ↑ Particle Data Group. "2006 Review of Particle Physics – Ω0
    c    "     (PDF). Retrieved 2008-04-20.
  8. ↑ 8.0 8.1 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