Omega baryons (often called simply omega particles) are a family of subatomic

hadrons In particle physics, a hadron is a composite subatomic particle made of two or more quarks held together by the strong nuclear force. Pronounced , the name is derived . They are analogous to molecules, which are held together by the electric ...

which are represented by the symbol and are either charge neutral or have a +2, +1 or −1

elementary charge The elementary charge, usually denoted by , is a fundamental physical constant, defined as the electric charge carried by a single proton (+1 ''e'') or, equivalently, the magnitude of the negative electric charge carried by a single electron, ...

. Additionally, they contain no up or down

quark A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nucleus, atomic nuclei ...

s. 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 field. This coupling is very close to unity; in the Standard ...

s are also not expected to be observed. This is because the

Standard Model The Standard Model of particle physics is the Scientific theory, theory describing three of the four known fundamental forces (electromagnetism, electromagnetic, weak interaction, weak and strong interactions – excluding gravity) in the unive ...

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 ra ...

of top quarks to be roughly , which is about a twentieth of the timescale necessary for the

strong interaction In nuclear physics and particle physics, the strong interaction, also called the strong force or strong nuclear force, is one of the four known fundamental interaction, fundamental interactions. It confines Quark, quarks into proton, protons, n ...

s required for hadronization, the process by which hadrons form from quarks and gluons. The first omega baryon was the , it was made of three

strange quark The strange quark or s quark (from its symbol, s) is the third lightest of all quarks, a type of elementary particle. Strange quarks are found in subatomic particles called hadrons. Examples of hadrons containing strange quarks include kaons (), ...

s, and was discovered in 1964. The discovery was a great triumph in the study of

quarks A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. All commonly o ...

, 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 theoretical physicist who played a preeminent role in the development of the theory of elementary particles. Gell-Mann introduced the concept of quarks as the funda ...

and, independently, by the

Israel Israel, officially the State of Israel, is a country in West Asia. It Borders of Israel, shares borders with Lebanon to the north, Syria to the north-east, Jordan to the east, Egypt to the south-west, and the Mediterranean Sea to the west. Isr ...

Yuval Ne'eman. 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 is an elementary particle found in composite subatomic particles called hadrons such as the J/psi meson and the charmed baryons created in particle accelerator collisions. Several bosons, including th ...

. 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 that give rise to the quantum numbers of the hadrons. The quark model underlies "flavor SU(3)", or the Eig ...

. 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. Isospin is also known as isobaric spin or isotopic spin. Isospin symmetry is a subset of the flavour symmetr ...

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

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

Recent discoveries

The particle is a "doubly strange"

baryon In particle physics, a baryon is a type of composite particle, composite subatomic particle that contains an odd number of valence quarks, conventionally three. proton, Protons and neutron, neutrons are examples of baryons; because baryons are ...

containing two strange quarks and a

bottom quark The bottom quark, beauty quark, or b quark, is an elementary particle of the third generation. It is a heavy quark with a charge of − ''e''. All quarks are described in a similar way by electroweak interaction and quantum chromodynamic ...

. 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 Fermilab, Fermi National Accelerator Laboratory (called ''Fermilab''), east of Batavia, Illinois, and was the highest energy particle collider unt ...

facility of the

Fermi National Accelerator Laboratory Fermi National Accelerator Laboratory (Fermilab), located in Batavia, Illinois, near Chicago, is a United States Department of Energy national laboratory specializing in high-energy particle physics. Fermilab's Main Injector, two miles (3.3 k ...

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

. The apparent discrepancy from the

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. 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 a particle physics detector collecting data at the Large Hadron Collider at CERN. LHCb specializes in the measurements of the parameters of CP violation in the interactions of b- and c-hadro ...

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