View source for Omega baryon

{{Short description|Subatomic hadron particle}}
{{redirect|Omega particle|usage of the term in ''Star Trek''|The Omega Directive}}
{{distinguish|Omega meson}}
{{Use dmy dates|date=February 2021}}
[[Image:Omega Baryon.svg|thumb|240px|[[Bubble chamber]] trace of the first observed Ω baryon event at Brookhaven National Laboratory, adapted from original tracing. The tracks of neutral particles (dashed lines) are not visible in the bubble chamber. The collision of a K<sup>−</sup> meson with a proton creates an Ω<sup>−</sup>, a K<sup>0</sup> and a K<sup>+</sup>. The Ω<sup>−</sup> decays into a π<sup>−</sup> and a Ξ<sup>0</sup>, which in turn decays into a Λ<sup>0</sup> and a π<sup>0</sup>. The Λ<sup>0</sup> decays into a proton and a π<sup>−</sup>. The π<sup>0</sup>, invisible due to its short lifetime, decays into two photons (γ), which in turn each create an [[Pair production|electron-positron pair]].]]
'''Omega baryons''' (often called simply omega particles) are a family of [[subatomic particle|subatomic]] [[hadrons]] which are represented by the symbol {{SubatomicParticle|Omega}} and are either charge [[neutral particle|neutral]] or have a +2, +1 or −1 [[elementary charge]]. Additionally, they contain no [[up quark|up]] or [[down quark|down]] [[quark]]s.<ref name=PDGnaming>{{cite web | author=Particle Data Group | author-link=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 |access-date=2011-12-26 }}</ref> Omega baryons containing [[top quark]]s are also 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}},<ref name=Quadt>
{{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
 |s2cid=121887478
 |url=https://cds.cern.ch/record/1339554
 |url-access=subscription
 }}</ref> which is about a twentieth of the timescale necessary for the [[strong interaction]]s required for [[hadronization]], the process by which hadrons form from quarks and gluons.

The earliest observed '''omega baryon''' was the {{SubatomicParticle|Omega-}}, made of three [[strange quark]]s. It was first observed in 1964.<ref>
{{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
|osti=12491965
 |display-authors=etal}}</ref> 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 [[United States|American]] [[physicist]] [[Murray Gell-Mann]] and, independently, by the [[Israel]]i [[physicist]] [[Yuval Ne'eman]]. A charmed omega particle ({{SubatomicParticle|Charmed Omega0}}) was discovered in 1985, in which a strange quark is replaced by a [[charm quark]]. The {{SubatomicParticle|Omega-}} decays only via the weak interaction and therefore has a relatively long lifetime.<ref>
{{cite web
 |author=R. Nave
 |title=The Omega baryon
 |url=http://hyperphysics.phy-astr.gsu.edu/hbase/particles/omega.html#c1
 |website=[[HyperPhysics]]
 |access-date=2009-11-26
}}</ref> [[Spin (physics)|Spin]] (''J'') and [[parity (physics)|parity]] (''P'') values for unobserved baryons are predicted by the [[quark model]].<ref>{{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|arxiv=hep-ph/9406359 |bibcode=1994PrPNP..33..787K|s2cid=118931787 }}</ref>

Since omega baryons do not have any up or down quarks, they all have [[isospin]] 0.

The naming convention of baryons has become such that those with no light (i.e. up or down) valence quarks are called omega baryons. By default, the quarks are strange quarks, but those with one or more the strange quarks replaced by charm or bottom quarks have a subscript c or b, respectively.  
==Omega baryons==
[[File:Quark structure omega.svg|thumb|194x194px|Quark structure of omega baryon ({{SubatomicParticle|Omega-}})]]
{| class="wikitable sortable"
|+Omega
|-
! class=unsortable|Particle
! Symbol
! Quark<br />content
! [[Rest mass]]<br />([[electron volt|MeV]]/[[speed of light|''c'']]<sup>2</sup>)
! [[Spin (physics)|J]]<sup>[[Parity (physics)|P]]</sup>
! [[charge (physics)|Q]]<br />([[elementary charge|''e'']])
! [[strangeness|S]]
! [[charm (quantum number)|C]]
! {{nowrap|[[bottomness|B']]}}
! [[Mean lifetime]]<br />([[second|s]])
! class=unsortable|Decays to
|-
| Omega<ref name=PDGOmega->{{cite web |author=Particle Data Group |author-link=Particle Data Group |url=http://pdg.lbl.gov/2007/listings/s024.pdf |title= 2006 Review of Particle Physics – {{SubatomicParticle|Omega-}} |access-date=2008-04-20 }}</ref>
| {{SubatomicParticle|Omega-}}
| {{SubatomicParticle|link=yes|Strange quark}}{{SubatomicParticle|link=yes|Strange quark}}{{SubatomicParticle|link=yes|Strange quark}}
| {{val|1672.45|0.29}}
| {{sfrac|3|2}}<sup>+</sup>
| −1
| −3
| 0
| 0
| {{val|8.21|0.11|e=-11}}
| {{nowrap|{{SubatomicParticle|link=yes|Lambda0}} + {{SubatomicParticle|link=yes|Kaon-}}}} or <br/> {{nowrap|{{SubatomicParticle|link=yes|Xi0}} + {{SubatomicParticle|link=yes|Pion-}}}} or <br /> {{nowrap|{{SubatomicParticle|link=yes|Xi-}} + {{SubatomicParticle|link=yes|Pion0}}}} <br />
|-
| Charmed omega<ref name=PDGCharmedOmega0>{{cite web |author=Particle Data Group |author-link=Particle Data Group |url=http://pdg.lbl.gov/2018/listings/rpp2018-list-omegac-zero.pdf |title={{SubatomicParticle|Charmed omega0}} listing – {{SubatomicParticle|Charmed Omega0}}|access-date=13 August 2018 }}</ref>
| {{SubatomicParticle|Charmed Omega0}}
| {{SubatomicParticle|link=yes|Strange quark}}{{SubatomicParticle|link=yes|Strange quark}}{{SubatomicParticle|link=yes|Charm quark}}
| {{val|2697.5|2.6}}
| {{sfrac|1|2}}<sup>+</sup>
| 0
| −2
| +1
| 0
| {{val|268|24|e=-15}}
| See [https://pdg.lbl.gov/2022/listings/contents_listings.html {{SubatomicParticle|Charmed omega0}} Decay Modes]
|-
| Bottom omega<ref name="CDF"/>
| {{SubatomicParticle|Bottom Omega-}}
| {{SubatomicParticle|link=yes|Strange quark}}{{SubatomicParticle|link=yes|Strange quark}}{{SubatomicParticle|link=yes|Bottom quark}}
| {{val|6054.4|6.8}}
| {{sfrac|1|2}}<sup>+</sup>
| −1
| −2
| 0
| −1
|{{val|1.13|0.53|e=-12}}
|{{nowrap|{{SubatomicParticle|Omega-}} + {{SubatomicParticle|link=yes|J/Psi}}}} (seen)
|-
| Double charmed omega†
| {{SubatomicParticle|Double charmed Omega+}}
| {{SubatomicParticle|link=yes|Strange quark}}{{SubatomicParticle|link=yes|Charm quark}}{{SubatomicParticle|link=yes|Charm quark}}
|
| {{sfrac|1|2}}<sup>+</sup>
| +1
| −1
| +2
| 0
|
|
|-
| Charmed bottom omega†
| {{SubatomicParticle|Charmed bottom Omega0}}
| {{SubatomicParticle|link=yes|Strange quark}}{{SubatomicParticle|link=yes|Charm quark}}{{SubatomicParticle|link=yes|Bottom quark}}
|
| {{sfrac|1|2}}<sup>+</sup>
| 0
| −1
| +1
| −1
|
|
|-
| Double bottom omega†
| {{SubatomicParticle|Double Bottom Omega-}}
| {{SubatomicParticle|link=yes|Strange quark}}{{SubatomicParticle|link=yes|Bottom quark}}{{SubatomicParticle|link=yes|Bottom quark}}
|
| {{sfrac|1|2}}<sup>+</sup>
| −1
| −1
| 0
| −2
|
|
|-
| Triple charmed omega†
| {{SubatomicParticle|Triple charmed Omega++}}
| {{SubatomicParticle|link=yes|Charm quark}}{{SubatomicParticle|link=yes|Charm quark}}{{SubatomicParticle|link=yes|Charm quark}}
|
| {{sfrac|3|2}}<sup>+</sup>
| +2
| 0
| +3
| 0
|
|
|-
| Double charmed bottom omega†
| {{SubatomicParticle|Double charmed bottom Omega+}}
| {{SubatomicParticle|link=yes|Charm quark}}{{SubatomicParticle|link=yes|Charm quark}}{{SubatomicParticle|link=yes|Bottom quark}}
|
| {{sfrac|1|2}}<sup>+</sup>
| +1
| 0
| +2
| −1
|
|
|-
| Charmed double bottom omega†
| {{SubatomicParticle|Charmed double bottom Omega0}}
| {{SubatomicParticle|link=yes|Charm quark}}{{SubatomicParticle|link=yes|Bottom quark}}{{SubatomicParticle|link=yes|Bottom quark}}
|
| {{sfrac|1|2}}<sup>+</sup>
| 0
| 0
| +1
| −2
|
|
|-
| Triple bottom omega†
| {{SubatomicParticle|Triple Bottom Omega-}}
| {{SubatomicParticle|link=yes|Bottom quark}}{{SubatomicParticle|link=yes|Bottom quark}}{{SubatomicParticle|link=yes|Bottom quark}}
|
| {{sfrac|3|2}}<sup>+</sup>
| −1
| 0
| 0
| −3
|
|
|-
|}
† Particle (or quantity, i.e. spin) has neither been observed nor indicated.<!--- ***** do not add top quark Omegas here – such baryons are not expected to exists since m_t > m_W + m_b ***** --->

==Recent discoveries==
The {{SubatomicParticle|Bottom Omega-}} particle is a "doubly [[strangeness|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|DØ]] experiment at the [[Tevatron]] facility of the [[Fermi National Accelerator Laboratory]].<ref>
{{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]]
 |access-date=2008-09-04
}}</ref><ref>
{{cite journal
 |author=V. Abazov ''et al.'' ([[DØ experiment|DØ Collaboration]])
 |year=2008
 |title=Observation of the doubly strange b baryon {{SubatomicParticle|Bottom Omega-}}
 |journal=[[Physical Review Letters]]
 |volume=101 |issue=23 |article-number=232002
 |arxiv=0808.4142
 |bibcode=2008PhRvL.101w2002A
 |doi=10.1103/PhysRevLett.101.232002
|pmid=19113541
 |s2cid=30481085
 }}</ref> 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 [[Collider Detector at Fermilab|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]].<ref name=CDF>
{{cite journal
 |author=T. Aaltonen ''et al.'' ([[Collider Detector at Fermilab|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 |article-number=072003
 |arxiv=0905.3123
 |bibcode=2009PhRvD..80g2003A
 |doi=10.1103/PhysRevD.80.072003
|hdl=1721.1/52706
 |s2cid=54189461
 }}</ref> [[Collider Detector at Fermilab|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.<ref name=LHCb>{{cite journal
 |author=R. Aaij ''et al.'' ([[LHCb|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 |article-number=182001
 |arxiv=1302.1072
 |bibcode=2013PhRvL.110r2001A
 |doi=10.1103/PhysRevLett.110.182001
|pmid=23683191
 |s2cid=22966047
 }}</ref>

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+}}.<ref>{{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}}</ref><ref>{{cite journal|author=R. Aaij ''et al.'' ([[LHCb|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|article-number=182001|arxiv=1703.04639|bibcode=2017PhRvL.118r2001A|doi=10.1103/PhysRevLett.118.182001|pmid=28524669|s2cid=610517}}</ref> The states are named {{SubatomicParticle|Charmed Omega}}(3000)<sup>0</sup>, {{SubatomicParticle|Charmed Omega}}(3050)<sup>0</sup>, {{SubatomicParticle|Charmed Omega}}(3066)<sup>0</sup>, {{SubatomicParticle|Charmed Omega}}(3090)<sup>0</sup> and {{SubatomicParticle|Charmed Omega}}(3119)<sup>0</sup>. 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==
{{Reflist|30em}}

==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-}}]
*[https://www.bbc.co.uk/programmes/p01z4p1j Strangeness Minus Three – BBC Horizon 1964]

{{Particles}}

[[Category:Baryons]]
[[Category:Murray Gell-Mann]]