Omega baryon

Omega baryon

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 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.

Contents

  • Omega baryons 1
  • Recent discoveries 2
  • See also 3
  • References 4
  • External links 5

Omega baryons

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 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 Decay ModesΩ0
c
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

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

References

  1. ^  
  2. ^ A. Quadt (2006). "Top quark physics at hadron colliders".  
  3. ^ V. E. Barnes; et al. (1964). "Observation of a Hyperon with Strangeness Minus Three" (PDF).  
  4. ^ R. Nave. "The Omega baryon".  
  5. ^ J. G. Körner, M. Krämer, and D. Pirjol (1994). "Heavy Baryons".  
  6. ^  
  7. ^ Particle Data Group. "Ω0
    c
    "2006 Review of Particle Physics – (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
    ".  
  9. ^ "Fermilab physicists discover "doubly strange" particle".  
  10. ^ V. Abazov et al. (DØ Collaboration) (2008). "Observation of the doubly strange b baryon Ω
    b
    ".  

External links

  • Ω, which happens to contain the complete decay chain of the ΩPicture of the first event containing the .
  • Ω
    b
    Science Daily – Discovery of the
  • Strangeness Minus Three - BBC Horizon 1964