The sigma baryons are a family of
subatomic
In physics, a subatomic particle is a particle smaller than 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 baryon, like ...
hadron
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 electri ...
particles which have two
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 from the first
flavour generation (
up and / or
down quarks), 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
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 ...
s, with total
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 ...
of 1, and can either be
neutral or have an
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, ...
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.
The third quark can hence be either a
strange
Strange may refer to:
Fiction
* Strange (comic book), a comic book limited series by Marvel Comics
* Strange (Marvel Comics), one of a pair of Marvel Comics characters known as The Strangers
* Adam Strange, a DC Comics superhero
* The title c ...
(symbols , , ), a
charm (symbols , , ), a
bottom (symbols , , ) or a
top
Top most commonly refers to:
* Top, a basic term of orientation, distinguished from bottom, front, back, and sides
* Spinning top, a ubiquitous traditional toy
* Top (clothing), clothing designed to be worn over the torso
* Mountain top, a moun ...
(symbols , , ) quark. However, the top sigmas are expected to never be observed, since 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 .
[
] This is about 20 times shorter than the timescale for
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, and therefore it does not
form hadrons.
List
The symbols encountered in these lists are: (''
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 ...
''), (''
total angular momentum
In quantum mechanics, the total angular momentum quantum number parametrises the total angular momentum of a given particle, by combining its orbital angular momentum and its intrinsic angular momentum (i.e., its spin).
If s is the particle's ...
''), (''
parity''), u (''
up quark
The up quark or u quark (symbol: u) is the lightest of all quarks, a type of elementary particle, and a significant constituent of matter. It, along with the down quark, forms the neutrons (one up quark, two down quarks) and protons (two up quark ...
''), d (''
down quark
The down quark (symbol: d) is a type of elementary particle, and a major constituent of matter. The down quark is the second-lightest of all quarks, and combines with other quarks to form composite particles called hadrons. Down quarks are most ...
''), s (''
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 (), ...
''), c (''
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 ...
''), t (''
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 ...
''), b (''
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 ...
''), (''
electric charge
Electric charge (symbol ''q'', sometimes ''Q'') is a physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative''. Like charges repel each other and ...
''), (''
strangeness
In particle physics, strangeness (symbol ''S'') is a property of particles, expressed as a quantum number, for describing decay of particles in strong and electromagnetic interactions that occur in a short period of time. The strangeness of a ...
''), (''
charmness''), (''
bottomness''), (''
topness''), as well as other subatomic particles (hover for name).
Antiparticles are not listed in the table; however, they simply would have all quarks changed to antiquarks (and vice versa), and , , , , , , would be of opposite signs. , , and values in red have not been firmly established by experiments, but 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 ...
and are consistent with the measurements.
[
]
= + sigma baryons
† The standard model predicts that this particle cannot exist.
/sup> PDG reports the resonance width (). Here the conversion is given instead.
/sup> The specific values of the name has not been decided yet, but will likely be close to (5810).
= + sigma baryons
† The standard model predicts that this particle cannot exist.
/sup> PDG reports the resonance width (). Here the conversion is given instead.
The following table compares the nearly-identical Lambda and neutral Sigma baryons:
See also
* Delta baryon
* Hyperon
* Lambda baryon
* List of mesons
: ''This list is of all known and predicted scalar, pseudoscalar and vector mesons. See list of particles for a more detailed list of particles found in particle physics.''
This article contains a list of mesons, unstable subatomic particles ...
* List of particles
This is a list of known and hypothesized microscopic particles in particle physics, condensed matter physics and cosmology.
Standard Model elementary particles
Elementary particles are particles with no measurable internal structure; that is, ...
* Nucleon
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.
Until the 1960s, nucleons were thought to be ele ...
* Omega baryon
Omega baryons (often called simply omega particles) are a family of subatomic hadrons which are represented by the symbol and are either charge neutral or have a +2, +1 or −1 elementary charge. Additionally, they contain no up or down qu ...
*
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