The omega baryons are a family of

subatomic In physical sciences, a subatomic particle is a particle that composes an atom. According to the Standard Model of particle physics, a subatomic particle can be either a composite particle, which is composed of other particles (for example, a pro ...

hadron In particle physics, a hadron (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the e ...

baryon In particle physics, a baryon is a type of composite subatomic particle which contains an odd number of valence quarks (at least 3). Baryons belong to the hadron family of particles; hadrons are composed of quarks. Baryons are also classif ...

) particles that are represented by the symbol and are either

neutral Neutral or neutrality may refer to: Mathematics and natural science Biology * Neutral organisms, in ecology, those that obey the unified neutral theory of biodiversity Chemistry and physics * Neutralization (chemistry), a chemical reaction in ...

or have a +2, +1 or −1 elementary charge. They are

s containing no up or down quarks. Omega baryons containing

top quark The top quark, sometimes also referred to as the truth quark, (symbol: t) is the most massive of all observed elementary particles. It derives its mass from its coupling to the Higgs Boson. This coupling y_ is very close to unity; in the Standard ...

s are not expected to be observed. This is because the Standard Model predicts the

mean lifetime A quantity is subject to exponential decay if it decreases at a rate proportional to its current value. Symbolically, this process can be expressed by the following differential equation, where is the quantity and ( lambda) is a positive rate ...

of top quarks to be roughly , 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 , made of three strange quarks, in 1964. 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 A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate cau ...

Murray Gell-Mann Murray Gell-Mann (; September 15, 1929 – May 24, 2019) was an American physicist who received the 1969 Nobel Prize in Physics for his work on the theory of elementary particles. He was the Robert Andrews Millikan Professor of Theoretical ...

and, independently, by the

Israel Israel (; he, יִשְׂרָאֵל, ; ar, إِسْرَائِيل, ), officially the State of Israel ( he, מְדִינַת יִשְׂרָאֵל, label=none, translit=Medīnat Yīsrāʾēl; ), is a country in Western Asia. It is situated ...

Yuval Ne'eman Yuval Ne'eman ( he, יובל נאמן, 14 May 1925 – 26 April 2006) was an Israeli theoretical physicist, military scientist, and politician. He was Minister of Science and Development in the 1980s and early 1990s. He was the President o ...

. Besides the , a charmed omega particle () was discovered in 1985, in which a strange quark is replaced by a

charm quark The charm quark, charmed quark or c quark (from its symbol, c) is the third-most massive of all quarks, a type of elementary particle. Charm quarks are found in hadrons, which are subatomic particles made of quarks. Examples of hadrons containin ...

. The decays only via the weak interaction and has therefore a relatively long lifetime. Spin (''J'') and parity (''P'') values for unobserved baryons are predicted by the

quark model In particle physics, the quark model is a classification scheme for hadrons in terms of their valence quarks—the quarks and antiquarks which give rise to the quantum numbers of the hadrons. The quark model underlies "flavor SU(3)", or the Ei ...

. Since omega baryons do not have any up or down quarks, they all have

isospin In nuclear physics and particle physics, isospin (''I'') is a quantum number related to the up- and down quark content of the particle. More specifically, isospin symmetry is a subset of the flavour symmetry seen more broadly in the interactions ...

Omega baryons

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

Recent discoveries

The particle is a "doubly strange"

containing two strange quarks and a

bottom quark The bottom quark or b quark, also known as the beauty quark, is a third-generation heavy quark with a charge of − ''e''. All quarks are described in a similar way by electroweak and quantum chromodynamics, but the bottom quark has exce ...

. A discovery of this particle was first claimed in September 2008 by physicists working on the DØ experiment at the

Tevatron The Tevatron was a circular particle accelerator (active until 2011) in the United States, at the Fermi National Accelerator Laboratory (also known as ''Fermilab''), east of Batavia, Illinois, and is the second highest energy particle collider ...

facility of the

Fermi National Accelerator Laboratory Fermi National Accelerator Laboratory (Fermilab), located just outside Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Since 2007, Fermilab has been operat ...

. However, the reported mass of was significantly higher than expected in the

. The apparent discrepancy from the Standard Model has since been dubbed the " puzzle". In May 2009, the CDF collaboration made public their results on the search for the based on analysis of a data sample roughly four times the size of the one used by the

DØ experiment The DØ experiment (sometimes written D0 experiment, or DZero experiment) was a worldwide collaboration of scientists conducting research on the fundamental nature of matter. DØ was one of two major experiments (the other was the CDF experim ...

. CDF measured the mass to be , 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 , 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 . In February 2013 the

LHCb The LHCb (Large Hadron Collider beauty) experiment is one of eight particle physics detector experiments collecting data at the Large Hadron Collider at CERN. LHCb is a specialized b-physics experiment, designed primarily to measure the paramet ...

collaboration published a measurement of the mass that is consistent with, but more precise than, the CDF result. In March 2017, the LHCb collaboration announced the observation of five new narrow states decaying to , where the was reconstructed in the decay mode . The states are named (3000)⁰, (3050)⁰, (3066)⁰, (3090)⁰ and (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.

Omega baryons

Recent discoveries

See also

References

External links