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 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. 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, 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. 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. Spin (J) and parity (P) values for unobserved baryons are predicted by the quark model.

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 (e)	S	C	B′	Mean lifetime (s)	Decays to
Omega	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	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	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 the Tevatron facility of the Fermi National Accelerator Laboratory. 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. 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

• Delta baryon
• Hyperon
• Lambda baryon
• List of mesons
• List of particles
• Nucleon
• Physics portal
• Sigma baryon
• Timeline of particle discoveries
• Xi baryon

External links

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