![](https://upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Omega_Baryon.svg/240px-Omega_Baryon.svg.png)
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
[edit]![](https://upload.wikimedia.org/wikipedia/commons/thumb/a/a0/Quark_structure_omega.svg/194px-Quark_structure_omega.svg.png)
Ω−
)
Particle | Symbol | Quark content |
Rest mass (MeV/c2) |
JP | Q (e) |
S | C | B' | Mean lifetime (s) |
Decays to |
---|---|---|---|---|---|---|---|---|---|---|
Omega[6] | Ω− |
s s s |
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 |
s s c |
2697.5±2.6 | 1/2+ | 0 | −2 | +1 | 0 | (268±24)×10−15 | See Ω0 c Decay Modes |
Bottom omega[8] | Ω− b |
s s b |
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 |
s c c |
1/2+ | +1 | −1 | +2 | 0 | |||
Charmed bottom omega† | Ω0 cb |
s c b |
1/2+ | 0 | −1 | +1 | −1 | |||
Double bottom omega† | Ω− bb |
s b b |
1/2+ | −1 | −1 | 0 | −2 | |||
Triple charmed omega† | Ω++ ccc |
c c c |
3/2+ | +2 | 0 | +3 | 0 | |||
Double charmed bottom omega† | Ω+ ccb |
c c b |
1/2+ | +1 | 0 | +2 | −1 | |||
Charmed double bottom omega† | Ω0 cbb |
c b b |
1/2+ | 0 | 0 | +1 | −2 | |||
Triple bottom omega† | Ω− bbb |
b b b |
3/2+ | −1 | 0 | 0 | −3 |
† Particle (or quantity, i.e. spin) has neither been observed nor indicated.
Recent discoveries
[edit]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+
c
K−
, where the
Ξ+
c was reconstructed in the decay mode
p
K−
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
[edit]- Delta baryon
- Hyperon
- Lambda baryon
- List of mesons
- List of particles
- Nucleon
- Physics portal
- Sigma baryon
- Timeline of particle discoveries
- Xi baryon
References
[edit]- ^ Particle Data Group. "2010 Review of Particle Physics – Naming scheme for hadrons" (PDF). Retrieved 26 December 2011.
- ^ 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. S2CID 121887478.
- ^ V. E. Barnes; et al. (1964). "Observation of a Hyperon with Strangeness Minus Three" (PDF). Physical Review Letters. 12 (8): 204. Bibcode:1964PhRvL..12..204B. doi:10.1103/PhysRevLett.12.204. OSTI 12491965.
- ^ R. Nave. "The Omega baryon". HyperPhysics. Retrieved 26 November 2009.
- ^ Körner, J.G; Krämer, M; Pirjol, D (1 January 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. S2CID 118931787.
- ^ Particle Data Group. "2006 Review of Particle Physics –
Ω−
" (PDF). Retrieved 20 April 2008. - ^ Particle Data Group. "
Ω0
c listing –
Ω0
c" (PDF). Retrieved 13 August 2018. - ^ 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): 072003. arXiv:0905.3123. Bibcode:2009PhRvD..80g2003A. doi:10.1103/PhysRevD.80.072003. hdl:1721.1/52706. S2CID 54189461. - ^ "Fermilab physicists discover "doubly strange" particle". Fermilab. 3 September 2008. Retrieved 4 September 2008.
- ^
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. PMID 19113541. S2CID 30481085. - ^ R. Aaij et al. (LHCb collaboration) (2013). "Measurement of the
Λ0
b,
Ξ−
b and
Ω−
b baryon masses". Physical Review Letters. 110 (18): 182001. arXiv:1302.1072. Bibcode:2013PhRvL.110r2001A. doi:10.1103/PhysRevLett.110.182001. PMID 23683191. S2CID 22966047. - ^ "LHCb observes an exceptionally large group of particles". CERN.
- ^ R. Aaij et al. (LHCb collaboration) (2017). "Observation of five new narrow
Ω0
c states decaying to
Ξ+
c
K−
". Physical Review Letters. 11801 (2017): 182001. arXiv:1703.04639. Bibcode:2017PhRvL.118r2001A. doi:10.1103/PhysRevLett.118.182001. PMID 28524669. S2CID 610517.