Omega baryon
Subatomic hadron particle From Wikipedia, the free encyclopedia
Omega baryons (often called simply omega particles) are a family of subatomic hadrons which are represented by the symbol Ω and are either charge neutral or have a +2, +1 or −1 elementary charge. Additionally, they contain no up or down quarks.[1] Omega baryons containing top quarks are also 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 necessary for the strong interactions required for hadronization, the process by which hadrons form from quarks and gluons.

The first omega baryon was the Ω−
, it was made of three strange quarks, and was discovered in 1964.[3] The discovery was a great triumph in the study of quarks, since it was found only after its existence, mass, and decay products had been predicted in 1961 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 1985, 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

)
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 | (268±24)×10−15 | 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
Summarize
Perspective
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 the Tevatron facility of the Fermi National Accelerator Laboratory.[9][10] However, the reported mass of 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. In February 2013 the LHCb collaboration published a measurement of the Ω−
b mass that is consistent with, but more precise than, the CDF result.[11]
In March 2017, the LHCb collaboration announced the observation of five new narrow Ω0
c states decaying to Ξ+
cK−
, where the Ξ+
c was reconstructed in the decay mode pK−
π+
.[12][13] The states are named Ω
c(3000)0, Ω
c(3050)0, Ω
c(3066)0, Ω
c(3090)0 and Ω
c(3119)0. Their masses and widths were reported, but their quantum numbers could not be determined due to the large background present in the sample.
See also
References
External links
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