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词条 Omega baryon
释义

  1. Omega baryons

  2. Recent discoveries

  3. See also

  4. References

  5. External links

{{redirect|Omega particle|the Star Trek episode|The Omega Directive}}

The omega baryons are a family of subatomic hadron (a baryon) particles that are represented by the symbol {{SubatomicParticle|Omega}} and are either neutral or have a +2, +1 or −1 elementary charge. They are baryons containing no up or down quarks.[1] 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 {{val|5|e=-25|u=s}},[2] 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 {{SubatomicParticle|Omega-}}, 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 in 1961 by the American physicist Murray Gell-Mann and, independently, by the Israeli physicist Yuval Ne'eman. Besides the {{SubatomicParticle|Omega-}}, a charmed omega particle ({{SubatomicParticle|Charmed Omega0}}) was discovered, in which a strange quark is replaced by a charm quark. The {{SubatomicParticle|Omega-}} 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

Omega
Particle Symbol Quark
content		 Rest mass
(MeV/c2)		 JP Q
(e)		 S CB′ Mean lifetime
(s)		Decays to
Omega[6]Omega-}}link=yes|Strange quark}}{{SubatomicParticle|link=yes|Strange quark}}{{SubatomicParticle|link=yes|Strange quark}}1672.45|0.29}}3|2}}+ −1 −3 0 08.21|0.11|e=-11}}{{SubatomicParticle|link=yes|Lambda0}} + {{SubatomicParticle|link=yes|Kaon-}}}} or
{{nowrap|{{SubatomicParticle|link=yes|Xi0}} + {{SubatomicParticle|link=yes|Pion-}}}} or
{{nowrap|{{SubatomicParticle|link=yes|Xi-}} + {{SubatomicParticle|link=yes|Pion0}}}}
Charmed omega[7]Charmed Omega0}}link=yes|Strange quark}}{{SubatomicParticle|link=yes|Strange quark}}{{SubatomicParticle|link=yes|Charm quark}}2697.5|2.6}}1|2}}+ 0 −2 +1 06.9|1.2|e=-14}}{{SubatomicParticle>Charmed omega0}} Decay Modes
Bottom omega[8]Bottom Omega-}}link=yes|Strange quark}}{{SubatomicParticle|link=yes|Strange quark}}{{SubatomicParticle|link=yes|Bottom quark}}6054.4|6.8}}1|2}}+ −1 −2 0 −11.13|0.53|e=-12}}{{SubatomicParticle|Omega-}} + {{SubatomicParticle|link=yes|J/Psi}}}} (seen)
Double charmed omega†Double charmed Omega+}}link=yes|Strange quark}}{{SubatomicParticle|link=yes|Charm quark}}{{SubatomicParticle|link=yes|Charm quark}}1|2}}+ +1 −1 +2 0
Charmed bottom omega†Charmed bottom Omega0}}link=yes|Strange quark}}{{SubatomicParticle|link=yes|Charm quark}}{{SubatomicParticle|link=yes|Bottom quark}}1|2}}+ 0 −1 +1 −1
Double bottom omega†Double Bottom Omega-}}link=yes|Strange quark}}{{SubatomicParticle|link=yes|Bottom quark}}{{SubatomicParticle|link=yes|Bottom quark}}1|2}}+ −1 −1 0 −2
Triple charmed omega†Triple charmed Omega++}}link=yes|Charm quark}}{{SubatomicParticle|link=yes|Charm quark}}{{SubatomicParticle|link=yes|Charm quark}}3|2}}+ +2 0 +3 0
Double charmed bottom omega†Double charmed bottom Omega+}}link=yes|Charm quark}}{{SubatomicParticle|link=yes|Charm quark}}{{SubatomicParticle|link=yes|Bottom quark}}1|2}}+ +1 0 +2 −1
Charmed double bottom omega†Charmed double bottom Omega0}}link=yes|Charm quark}}{{SubatomicParticle|link=yes|Bottom quark}}{{SubatomicParticle|link=yes|Bottom quark}}1|2}}+ 0 0 +1 −2
Triple bottom omega†Triple Bottom Omega-}}link=yes|Bottom quark}}{{SubatomicParticle|link=yes|Bottom quark}}{{SubatomicParticle|link=yes|Bottom quark}}3|2}}+ −1 0 0 −3

† Particle (or quantity, i.e. spin) has neither been observed nor indicated.

Recent discoveries

The {{SubatomicParticle|Bottom Omega-}} 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.[8][9] However, the reported mass of {{val|6165|16|ul=MeV/c2}} was significantly higher than expected in the quark model. The apparent discrepancy from the Standard Model has since been dubbed the "{{SubatomicParticle|Bottom Omega}} puzzle". In May 2009, the CDF collaboration made public their results on the search for the {{SubatomicParticle|Bottom Omega-}} based on analysis of a data sample roughly four times the size of the one used by the DØ experiment.[10] CDF measured the mass to be {{val|6054.4|6.8|u=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 {{val|111|18|u=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 {{SubatomicParticle|Bottom Omega-}}. In February 2013 the LHCb collaboration published a measurement of the {{SubatomicParticle|Bottom Omega-}} 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 {{SubatomicParticle|Charmed Omega0}} states decaying to {{SubatomicParticle|Charmed Xi+}}{{SubatomicParticle|Kaon-}}, where the {{SubatomicParticle|Charmed Xi+}} was reconstructed in the decay mode {{SubatomicParticle|proton}}{{SubatomicParticle|Kaon-}}{{SubatomicParticle|pion+}}.[12][13] The states are named {{SubatomicParticle|Charmed Omega}}(3000)0, {{SubatomicParticle|Charmed Omega}}(3050)0, {{SubatomicParticle|Charmed Omega}}(3066)0, {{SubatomicParticle|Charmed Omega}}(3090)0 and {{SubatomicParticle|Charmed Omega}}(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

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

References

1. ^{{cite web | author=Particle Data Group |url=http://pdg.lbl.gov/2011/reviews/rpp2011-rev-naming-scheme-hadrons.pdf |title= 2010 Review of Particle Physics – Naming scheme for hadrons |accessdate=2011-12-26 }}
2. ^{{cite journal |author=A. Quadt |year=2006 |title=Top quark physics at hadron colliders |journal=European Physical Journal C |volume=48 |issue=3 |pages=835–1000 |bibcode = 2006EPJC...48..835Q |doi=10.1140/epjc/s2006-02631-6 |url=http://cds.cern.ch/record/1339554 }}
3. ^{{cite journal |author=V. E. Barnes|year=1964 |title=Observation of a Hyperon with Strangeness Minus Three |url=http://teachers.web.cern.ch/teachers/archiv/HST2001/bubblechambers/omegaminus.pdf |journal=Physical Review Letters |volume=12 |issue=8 |page=204 |bibcode = 1964PhRvL..12..204B |doi = 10.1103/PhysRevLett.12.204|display-authors=etal}}
4. ^{{cite web |author=R. Nave |year= |title=The Omega baryon |url=http://hyperphysics.phy-astr.gsu.edu/hbase/particles/omega.html#c1 |website=HyperPhysics |accessdate=2009-11-26}}
5. ^{{Cite journal|date=1994-01-01|title=Heavy baryons |journal=Progress in Particle and Nuclear Physics |volume=33|pages=787–868|doi=10.1016/0146-6410(94)90053-1 |last1=Körner|first1=J.G|last2=Krämer|first2=M|last3=Pirjol|first3=D}}
6. ^{{cite web |author=Particle Data Group |url=http://pdg.lbl.gov/2007/listings/s024.pdf |title= 2006 Review of Particle Physics – {{SubatomicParticle|Omega-}} |accessdate=2008-04-20 }}
7. ^{{cite web |author=Particle Data Group |url=http://pdg.lbl.gov/2018/listings/rpp2018-list-omegac-zero.pdf |title={{SubatomicParticle|Charmed omega0}} listing – {{SubatomicParticle|Charmed Omega0}}|accessdate=13 Aug 2018 }}
8. ^{{cite web |date=3 September 2008 |title=Fermilab physicists discover "doubly strange" particle |url=http://www.fnal.gov/pub/presspass/press_releases/Dzero_Omega-sub-b.html |publisher=Fermilab |accessdate=2008-09-04}}
9. ^{{cite journal |author=V. Abazov et al. (DØ Collaboration) |year=2008 |title=Observation of the doubly strange b baryon {{SubatomicParticle|Bottom Omega-}} |journal=Physical Review Letters |volume=101 |issue=23 |page=232002 |arxiv=0808.4142 |bibcode=2008PhRvL.101w2002A |doi=10.1103/PhysRevLett.101.232002|pmid=19113541 }}
10. ^1 {{cite journal |author=T. Aaltonen et al. (CDF Collaboration) |year=2009 |title=Observation of the {{SubatomicParticle|Bottom Omega-}} and Measurement of the Properties of the {{SubatomicParticle|Bottom Xi-}} and {{SubatomicParticle|Bottom Omega-}} |journal=Physical Review D |volume=80 |issue=7 |pages=072003 |arxiv=0905.3123 |bibcode=2009PhRvD..80g2003A |doi=10.1103/PhysRevD.80.072003|hdl=1721.1/52706 }}
11. ^{{cite journal |author=R. Aaij et al. (LHCb collaboration) |year=2013 |title=Measurement of the {{SubatomicParticle|Bottom Lambda0}}, {{SubatomicParticle|Bottom Xi-}} and {{SubatomicParticle|Bottom Omega-}} baryon masses |journal=Physical Review Letters |volume=110 |issue=18 |page=182001 |arxiv=1302.1072 |bibcode=2013PhRvL.110r2001A |doi=10.1103/PhysRevLett.110.182001|pmid=23683191 }}
12. ^{{cite web|title=LHCb observes an exceptionally large group of particles|publisher=CERN|url=http://home.cern/about/updates/2017/03/lhcb-observes-exceptionally-large-group-particles}}
13. ^{{cite journal|author=R. Aaij et al. (LHCb collaboration)|title=Observation of five new narrow {{SubatomicParticle|Charmed Omega0}} states decaying to {{SubatomicParticle|Charmed Xi+}}{{SubatomicParticle|Kaon-}}|year=2017|journal=Physical Review Letters|volume=11801|issue=2017|pages=182001|arxiv=1703.04639|bibcode=2017PhRvL.118r2001A|doi=10.1103/PhysRevLett.118.182001|pmid=28524669}}

External links

  • [https://www.flickr.com/photos/brookhavenlab/3148786892/in/album-72157611796003039/ Picture of the first event containing the {{SubatomicParticle|Omega-}}, which happens to contain the complete decay chain of the {{SubatomicParticle|Omega-}}].
  • [https://www.sciencedaily.com/releases/2008/09/080903172201.htm Science Daily – Discovery of the {{SubatomicParticle|Bottom Omega-}}]
  • Strangeness Minus Three - BBC Horizon 1964
{{Particles}}{{Use dmy dates|date=July 2011}}

1 : Baryons
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