Omega (Ω) baryons are baryons containing neither up nor down quarks. The first Omega discovered was the Ω−, made of three strange quarks was discovered in 1964.[1]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 already been predicted. Besides the Ω−, a charmed Omega particle (Ω0c) 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.[2] Spin (J) and parity (P) values for unobserved baryons are predicted by the quark model.[3]
Since Omega baryons do not have any up or down quarks, they all have isospin 0.
Contents |
Omega baryons
| Particle | Symbol | Quark content |
Rest mass MeV/c2 |
JP | Q | S | C | B | Mean lifetime s |
Decays to |
|---|---|---|---|---|---|---|---|---|---|---|
| Omega[4] | 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[5] | Ω0c | ssc | 2697.5±2.6 | 1⁄2+ | 0 | −2 | +1 | 0 | 6.9±1.2×10−14 | See Ω0c Decay Modes |
| Bottom Omega [6] | 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† | Ω0cb | 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† | Ω0cbb | 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 Ωb 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.[7][8] 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 "Ωb 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 DZero experiment.[9] 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
- ^ V.E. Barnes et al. (1964). "Observation of a Hyperon with Strangeness Number Three". Physical Review Letters 12 (8): p.204. http://teachers.web.cern.ch/teachers/archiv/HST2001/bubblechambers/omegaminus.pdf.
- ^ R. Nave. "The Omega baryon". http://hyperphysics.phy-astr.gsu.edu/hbase/particles/omega.html#c1. Retrieved 2009-11-26.
- ^ J. G. Körner, M. Krämer, and D. Pirjol (1994). "Heavy Baryons". Progress in Particle and Nuclear Physics 33: 787–868. doi:. arΧiv:hep-ph/9406359.
- ^ "Particle Data Groups: 2006 Review of Particle Physics - Omega-" (PDF). http://pdg.lbl.gov/2007/listings/s024.pdf. Retrieved 2008-04-20.
- ^ "Particle Data Groups: 2006 Review of Particle Physics - Charmed Omega0" (PDF). http://pdg.lbl.gov/2007/listings/s047.pdf. Retrieved 2008-04-20.
- ^ "Observation of the Omega_b^- and Measurement of the Properties of the Xi_b^- and Omega_b^-". http://arxiv.org/abs/0905.3123. Retrieved 2009-05-19.
- ^ "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.
- ^ D0 Collaboration; Abazov (2008). "Observation of the doubly strange b baryon Omega_b-, Fermilab-Pub-08/335-E". arΧiv:0808.4142 [hep-ex].
- ^ CDF Collaboration; Aaltonen (2009). "Observation of the Ω−b and Measurement of the Properties of the Ξ−b and Ω−b". arΧiv:0905.3123 [hep-ex].
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
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