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In particle physics, a hyperon is any baryon containing one or more strange quarks, but no charm, bottom, or top quark. [1] This form of matter may exist in a stable form within the core of some neutron stars. [2] Hyperons are sometimes generically represented by the symbol Y. [3]
The first research into hyperons happened in the 1950s and spurred physicists on to the creation of an organized classification of particles.
The term was coined by French physicist Louis Leprince-Ringuet in 1953, [4] [5] and announced for the first time at the cosmic ray conference at Bagnères de Bigorre in July of that year, agreed upon by Leprince-Ringuet, Bruno Rossi, C.F. Powell, William B. Fretter and Bernard Peters. [6]
Today, research in this area is carried out on data taken at many facilities around the world, including CERN, Fermilab, SLAC, JLAB, Brookhaven National Laboratory, KEK, GSI and others. Physics topics include searches for CP violation, measurements of spin, studies of excited states (commonly referred to as spectroscopy), and hunts for exotic forms such as pentaquarks and dibaryons.
Being baryons, all hyperons are fermions. That is, they have half-integer spin and obey Fermi–Dirac statistics. Hyperons all interact via the strong nuclear force, making them types of hadron. They are composed of three light quarks, at least one of which is a strange quark, which makes them strange baryons.
Excited hyperon resonances and ground-state hyperons with a '*' included in their notation decay via the strong interaction. For Ω⁻ as well as the lighter hyperons this decay mode is not possible given the particle masses and the conservation of flavor and isospin necessary in strong interactions. Instead, these decay weakly with non-conserved parity. An exception to this is the Σ⁰ which decays electromagnetically into Λ on account of carrying the same flavor quantum numbers. The type of interaction through which these decays occur determine the average lifetime, which is why weakly decaying hyperons are significantly more long-lived than those that decay through strong or electromagnetic interactions. [7]
| Particle | Symbol | Makeup | Rest mass (MeV/ c 2) | Isospin, I | Spin, parity, J P | Q (e) | S | C | B' | Mean lifetime (s) | Commonly decays to |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Lambda [8] | Λ0 | u d s | 1 115.683(6) | 0 | 1⁄2+ | 0 | −1 | 0 | 0 | 2.60×10−10 [9] | p+ + π− or n0 + π0 |
| Lambda resonance [10] | Λ (1405) | u d s | 1 405.1(+1.3 -1.0) | 0 | 1⁄2− | 0 | −1 | 0 | 0 | Σ + π | |
| Lambda resonance [11] | Λ (1520) | u d s | 1 519(1) | 0 | 3⁄2− | 0 | −1 | 0 | 0 | N + K or Σ + π or Λ + 2 π | |
| Sigma [12] | Σ+ | u u s | 1 189.37(7) | 1 | 1⁄2+ | +1 | −1 | 0 | 0 | (8.018±0.026)×10−11 | p+ + π0 or n0 + π+ |
| Sigma [13] | Σ0 | u d s | 1 192.642(24) | 1 | 1⁄2+ | 0 | −1 | 0 | 0 | (7.4±0.7)×10−20 | Λ0 + γ |
| Sigma [14] | Σ− | d d s | 1 197.449(30) | 1 | 1⁄2+ | −1 | −1 | 0 | 0 | (1.479±0.011)×10−10 | n0 + π− |
| Sigma resonance [15] | Σ∗+ (1385) | u u s | 1 382.8(4) | 1 | 3⁄2+ | +1 | −1 | 0 | 0 | Λ + π or Σ + π | |
| Sigma resonance [15] | Σ∗0 (1385) | u d s | 1 383.7±1.0 | 1 | 3⁄2+ | 0 | −1 | 0 | 0 | Λ + π or Σ + π | |
| Sigma resonance [15] | Σ∗− (1385) | d d s | 1 387.2(5) | 1 | 3⁄2+ | −1 | −1 | 0 | 0 | Λ + π or Σ + π | |
| Xi [16] | Ξ0 | u s s | 1 314.86(20) | 1⁄2 | 1⁄2+ | 0 | −2 | 0 | 0 | (2.90±0.09)×10−10 | Λ0 + π0 |
| Xi [17] | Ξ− | d s s | 1 321.71(7) | 1⁄2 | 1⁄2+ | −1 | −2 | 0 | 0 | (1.639±0.015)×10−10 | Λ0 + π− |
| Xi resonance [18] | Ξ∗0 (1530) | u s s | 1 531.80(32) | 1⁄2 | 3⁄2+ | 0 | −2 | 0 | 0 | Ξ + π | |
| Xi resonance [18] | Ξ∗− (1530) | d s s | 1 535.0(6) | 1⁄2 | 3⁄2+ | −1 | −2 | 0 | 0 | Ξ + π | |
| Omega [19] | Ω− | s s s | 1 672.45(29) | 0 | 3⁄2+ | −1 | −3 | 0 | 0 | (8.21±0.11)×10−11 | Λ0 + K− or Ξ0 + π− or Ξ− + π0 |
Notes:
In particle physics, a baryon is a type of composite subatomic particle, including the proton and the neutron, that contains an odd number of valence quarks, conventionally three. Baryons belong to the hadron family of particles; hadrons are composed of quarks. Baryons are also classified as fermions because they have half-integer spin.
In particle physics, a hadron is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules, which are held together by the electric force. Most of the mass of ordinary matter comes from two hadrons: the proton and the neutron, while most of the mass of the protons and neutrons is in turn due to the binding energy of their constituent quarks, due to the strong force.
In physics and chemistry, a nucleon is either a proton or a neutron, considered in its role as a component of an atomic nucleus. The number of nucleons in a nucleus defines the atom's mass number.
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 observable matter is composed of up quarks, down quarks and electrons. Owing to a phenomenon known as color confinement, quarks are never found in isolation; they can be found only within hadrons, which include baryons and mesons, or in quark–gluon plasmas. For this reason, much of what is known about quarks has been drawn from observations of hadrons.
The strange quark or s quark 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, strange D mesons, Sigma baryons, and other strange particles.
Omega baryons 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. 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, 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 bottom quark, beauty quark, or b quark, is an elementary particle of the third generation. It is a heavy quark with a charge of −1/3 e.
A pentaquark is a human-made subatomic particle, consisting of four quarks and one antiquark bound together; they are not known to occur naturally, or exist outside of experiments specifically carried out to create them.
In particle physics, a kaon, also called a K meson and denoted
K
, is any of a group of four mesons distinguished by a quantum number called strangeness. In the quark model they are understood to be bound states of a strange quark and an up or down antiquark.
In particle physics, the hyperchargeY of a particle is a quantum number conserved under the strong interaction. The concept of hypercharge provides a single charge operator that accounts for properties of isospin, electric charge, and flavour. The hypercharge is useful to classify hadrons; the similarly named weak hypercharge has an analogous role in the electroweak interaction.
In particle physics, exotic baryons are a type of hadron with half-integer spin, but with a quark content different from the three quarks (qqq) present in conventional baryons. An example would be pentaquarks, consisting of four quarks and one antiquark (qqqqq̅).
A hypernucleus is similar to a conventional atomic nucleus, but contains at least one hyperon in addition to the normal protons and neutrons. Hyperons are a category of baryon particles that carry non-zero strangeness quantum number, which is conserved by the strong and electromagnetic interactions.
In physics, the eightfold way is an organizational scheme for a class of subatomic particles known as hadrons that led to the development of the quark model. Both the American physicist Murray Gell-Mann and the Israeli physicist Yuval Ne'eman independently and simultaneously proposed the idea in 1961. The name comes from Gell-Mann's (1961) paper and is an allusion to the Noble Eightfold Path of Buddhism.
In particle physics, flavour or flavor refers to the species of an elementary particle. The Standard Model counts six flavours of quarks and six flavours of leptons. They are conventionally parameterized with flavour quantum numbers that are assigned to all subatomic particles. They can also be described by some of the family symmetries proposed for the quark-lepton generations.
The Xi baryons or cascade particles are a family of subatomic hadron particles which have the symbol Ξ and may have an electric charge of +2 e, +1 e, 0, or −1 e, where e is the elementary charge.
The lambda baryons (Λ) are a family of subatomic hadron particles containing one up quark, one down quark, and a third quark from a higher flavour generation, in a combination where the quantum wave function changes sign upon the flavour of any two quarks being swapped. They are thus baryons, with total isospin of 0, and have either neutral electric charge or the elementary charge +1.
The sigma baryons are a family of subatomic hadron particles which have two quarks from the first flavour generation, and a third quark from a higher flavour generation, in a combination where the wavefunction sign remains constant when any two quark flavours are swapped. They are thus baryons, with total isospin of 1, and can either be neutral or have an elementary charge of +2, +1, 0, or −1. They are closely related to the lambda baryons, which differ only in the wavefunction's behaviour upon flavour exchange.
A strangelet is a hypothetical particle consisting of a bound state of roughly equal numbers of up, down, and strange quarks. An equivalent description is that a strangelet is a small fragment of strange matter, small enough to be considered a particle. The size of an object composed of strange matter could, theoretically, range from a few femtometers across to arbitrarily large. Once the size becomes macroscopic, such an object is usually called a strange star. The term "strangelet" originates with Edward Farhi and Robert Jaffe in 1984. It has been theorized that strangelets can convert matter to strange matter on contact. Strangelets have also been suggested as a dark matter candidate.
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