Omega baryon

"Omega particle" redirects here. For the Star Trek particle, 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^{[citation needed]}. 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.^[1] 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.^[2] 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.^[3] Spin (J) and parity (P) values for unobserved baryons are predicted by the quark model.^[4]

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[5]	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[6]	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 [7]	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 DZero experiment at the Fermi National Accelerator Laboratory.^[8][9] 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.^[7] 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.

See also

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

References

1. ^ 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. 
2. ^ V. E. Barnes et al. (1964). "Observation of a Hyperon with Strangeness Number Three". Physical Review Letters 12 (8): 204. Bibcode 1964PhRvL..12..204B. doi:10.1103/PhysRevLett.12.204. http://teachers.web.cern.ch/teachers/archiv/HST2001/bubblechambers/omegaminus.pdf. 
3. ^ R. Nave. "The Omega baryon". HyperPhysics. http://hyperphysics.phy-astr.gsu.edu/hbase/particles/omega.html#c1. Retrieved 2009-11-26. 
4. ^ 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. 
5. ^ Particle Data Group. "2006 Review of Particle Physics - Ω−
   ". http://pdg.lbl.gov/2007/listings/s024.pdf. Retrieved 2008-04-20. 
6. ^ Particle Data Group. "2006 Review of Particle Physics - Ω0
   c". http://pdg.lbl.gov/2007/listings/s047.pdf. Retrieved 2008-04-20. 
7. ^ ^{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". Physical Review D 80 (7). arXiv:0905.3123. Bibcode 2009PhRvD..80g2003A. doi:10.1103/PhysRevD.80.072003. 
8. ^ "Fermilab physicists discover "doubly strange" particle". Fermilab. 3 September 2008. http://www.fnal.gov/pub/presspass/press_releases/Dzero_Omega-sub-b.html. Retrieved 2008-09-04. 
9. ^ 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

• Picture of the first event event containing the Ω−
  , which happens to be containing the complete decay chain of the Ω−
  .
• Science Daily - Discovery of the Ω−
  b