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 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 |
| 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 |
| 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.
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 DZero experiment at the Fermi National Accelerator Laboratory.[9][10] However, the reported mass, 6,165±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 6,054.4±6.8 MeV/c2 in excellent agreement with Standard Model prediction. No signal has been observed at DZero 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.
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