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| title | chunk | source | category | tags | date_saved | instance |
|---|---|---|---|---|---|---|
| List of particles | 2/3 | https://en.wikipedia.org/wiki/List_of_particles | reference | science, encyclopedia | 2026-05-05T08:22:02.237050+00:00 | kb-cron |
Ordinary mesons are made up of a valence quark and a valence antiquark. Because mesons have integer spin (0 or 1) and are not themselves elementary particles, they are classified as "composite" bosons, although being made of elementary fermions. Examples of mesons include the pion, kaon, and the J/ψ. In quantum hadrodynamics, mesons mediate the residual strong force between nucleons. At one time or another, positive signatures have been reported for all of the following exotic mesons but their existences have yet to be confirmed.
A tetraquark consists of two valence quarks and two valence antiquarks; A glueball is a bound state of gluons with no valence quarks; Hybrid mesons consist of one or more valence quark–antiquark pairs and one or more real gluons.
=== Atomic nuclei ===
Atomic nuclei typically consist of protons and neutrons, although exotic nuclei may consist of other baryons, such as hypertriton which contains a hyperon. These baryons (protons, neutrons, hyperons, etc.) which comprise the nucleus are called nucleons. Each type of nucleus is called a "nuclide", and each nuclide is defined by the specific number of each type of nucleon.
"Isotopes" are nuclides which have the same number of protons but differing numbers of neutrons. Conversely, "isotones" are nuclides which have the same number of neutrons but differing numbers of protons. "Isobars" are nuclides which have the same total number of nucleons but which differ in the number of each type of nucleon. Nuclear reactions can change one nuclide into another.
=== Atoms ===
Atoms are the smallest neutral particles into which matter can be divided by chemical reactions. An atom consists of a small, heavy nucleus surrounded by a relatively large, light cloud of electrons. An atomic nucleus consists of 1 or more protons and 0 or more neutrons. Protons and neutrons are, in turn, made of quarks. Each type of atom corresponds to a specific chemical element. To date, 118 elements have been discovered or created. Exotic atoms may be composed of particles in addition to or in place of protons, neutrons, and electrons, such as hyperons or muons. Examples include pionium (π− π+) and quarkonium atoms.
==== Leptonic atoms ==== Leptonic atoms, named using -onium, are exotic atoms constituted by the bound state of a lepton and an antilepton. Examples of such atoms include positronium (e− e+), muonium (e− μ+), and "true muonium" (μ− μ+). Of these positronium and muonium have been experimentally observed, while "true muonium" remains only theoretical.
=== Molecules ===
Molecules are the smallest particles into which a substance can be divided while maintaining the chemical properties of the substance. Each type of molecule corresponds to a specific chemical substance. A molecule is a composite of two or more atoms. Atoms are combined in a fixed proportion to form a molecule. Molecule is one of the most basic units of matter.
=== Ions === Ions are charged atoms (monatomic ions) or molecules (polyatomic ions). They include cations which have a net positive charge, and anions which have a net negative charge.
=== Other categories === Goldstone bosons are a massless excitation of a field that has been spontaneously broken. The pions are quasi-goldstone bosons (quasi- because they are not exactly massless) of the broken chiral isospin symmetry of quantum chromodynamics. Parton, is a generic term coined by Feynman for the sub-particles making up a composite particle – at that time a baryon – hence, it originally referred to what are now called "quarks" and "gluons". Odderon, a particle composed of an odd number of gluons, detected in 2021.
== Quasiparticles ==
Quasiparticles are effective particles that exist in many particle systems. The field equations of condensed matter physics are remarkably similar to those of high energy particle physics. As a result, much of the theory of particle physics applies to condensed matter physics as well; in particular, there are a selection of field excitations, called quasi-particles, that can be created and explored. These include:
Anyons are a generalization of fermions and bosons in two-dimensional systems like sheets of graphene that obeys braid statistics. Excitons are bound states of an electron and a hole. Magnons are coherent excitations of electron spins in a material. Phonons are vibrational modes in a crystal lattice. Plasmons are coherent excitations of a plasma. Polaritons are mixtures of photons with other quasi-particles. Polarons are moving, charged (quasi-) particles that are surrounded by ions in a material.
== Hypothetical particles ==
=== Graviton ===
The graviton is a hypothetical particle that has been included in some extensions to the Standard Model to mediate the gravitational force. It is in a peculiar category between known and hypothetical particles: as an unobserved particle that is not predicted by, nor required for the Standard Model, it belongs in the table of hypothetical particles. But gravitational force itself is a certainty, and expressing that known force in the framework of a quantum field theory requires a boson to mediate it. If it exists, the graviton is expected to be massless because the gravitational force has a very long range, and appears to propagate at the speed of light. The graviton must be a spin-2 boson because the source of gravitation is the stress–energy tensor, a second-order tensor (compared with electromagnetism's spin-1 photon, the source of which is the four-current, a first-order tensor). Additionally, it can be shown that any massless spin-2 field would give rise to a force indistinguishable from gravitation, because a massless spin-2 field would couple to the stress–energy tensor in the same way that gravitational interactions do. This result suggests that, if a massless spin-2 particle is discovered, it must be the graviton.
=== Dark matter candidates ===
Many hypothetical particle candidates for dark matter have been proposed like weakly interacting massive particles (WIMP), weakly interacting slender particles (WISP), or feebly interacting particles (FIP).
=== Dark energy candidates ===
Hypothetical particle candidates to explain dark energy include the chameleon particle and the acceleron.