List of particles

This article includes a list of the different types of atomic and sub-atomic particles found or hypothesized to exist in the whole of the universe, categorized by type. Properties of the various particles listed are also given, as well as the laws that the particles follow. For individual lists of the different particles, see the list below.

Elementary particles

Elementary particles are particles with no measurable internal structure; that is, it is unknown whether they are composed of other particles.[1] They are the fundamental objects of quantum field theory. Many families and sub-families of elementary particles exist. Elementary particles are classified according to their spin. Fermions have half-integer spin while bosons have integer spin. All the particles of the Standard Model have been experimentally observed, recently including the Higgs boson.[2][3] Many other hypothetical elementary particles, such as the graviton, have been proposed, but not observed experimentally.

Fermions

Fermions are one of the two fundamental classes of particles, the other being bosons. Fermion particles are described by Fermi–Dirac statistics and have quantum numbers described by the Pauli exclusion principle. They include the quarks and leptons, as well as any composite particles consisting of an odd number of these, such as all baryons and many atoms and nuclei.

Fermions have half-integer spin; for all known elementary fermions this is ​12. All known fermions, except neutrinos, are also Dirac fermions; that is, each known fermion has its own distinct antiparticle. It is not known whether the neutrino is a Dirac fermion or a Majorana fermion.[4] Fermions are the basic building blocks of all matter. They are classified according to whether they interact via the strong interaction or not. In the Standard Model, there are 12 types of elementary fermions: six quarks and six leptons.

Quarks

Quarks are the fundamental constituents of hadrons and interact via the strong interaction. Quarks are the only known carriers of fractional charge, but because they combine in groups of three (baryons) or in pairs of one quark and one antiquark (mesons), only integer charge is observed in nature. Their respective antiparticles are the antiquarks, which are identical except that they carry the opposite electric charge (for example the up quark carries charge +​23, while the up antiquark carries charge −​23), color charge, and baryon number. There are six flavors of quarks; the three positively charged quarks are called "up-type quarks" while the three negatively charged quarks are called "down-type quarks".

Quarks
Name Symbol Antiparticle Charge
(e)
Mass (MeV/c2) [5] Spin
up u
u
+​23 2.2+0.6
−0.4
12
down d
d
−​13 4.6+0.5
−0.4
12
charm c
c
+​23 1280±30 12
strange s
s
−​13 96+8
−4
12
top t
t
+​23 173,100±600 12
bottom b
b
−​13 4,180+40
−30
12

Leptons

Leptons do not interact via the strong interaction. Their respective antiparticles are the antileptons, which are identical, except that they carry the opposite electric charge and lepton number. The antiparticle of an electron is an antielectron, which is nearly always called a "positron" for historical reasons. There are six leptons in total; the three charged leptons are called "electron-like leptons", while the neutral leptons are called "neutrinos". Neutrinos are known to oscillate, so that neutrinos of definite flavor do not have definite mass, rather they exist in a superposition of mass eigenstates. The hypothetical heavy right-handed neutrino, called a "sterile neutrino", has been left off the list.

Leptons
Name Symbol Antiparticle Charge
(e)
Mass (MeV/c2) [5]
Electron
e

e+
−1 0.511[note 1]
Electron neutrino
ν
e

ν
e
0 < 0.0000022
Muon
μ

μ+
−1 105.7[note 2]
Muon neutrino
ν
μ

ν
μ
0 < 0.170
Tau
τ

τ+
−1 1,776.86±0.12
Tau neutrino
ν
τ

ν
τ
0 < 15.5
  1. ^ The electron mass is known very precisely as 0.5109989461±0.0000000031 MeV
  2. ^ The muon mass is known very precisely as 105.6583745±0.0000024 MeV

Bosons

Bosons are one of the two fundamental classes of particles, the other being fermions. Bosons are characterized by Bose–Einstein statistics and all have integer spins. Bosons may be either elementary, like photons and gluons, or composite, like mesons.

According to the Standard Model the elementary bosons are:

Name Symbol Antiparticle Charge (e) Spin Mass (GeV/c2) [5] Interaction mediated Observed
Photon γ Self 0 1 0 Electromagnetism Yes
W boson
W

W+
−1 1 80.385±0.015 Weak interaction Yes
Z boson
Z
Self 0 1 91.1875±0.0021 Weak interaction Yes
Gluon
g
Self 0 1 0 Strong interaction Yes
Higgs boson
H0
Self 0 0 125.09±0.24 Mass Yes

The Higgs boson is postulated by the electroweak theory primarily to explain the origin of particle masses. In a process known as the "Higgs mechanism", the Higgs boson and the other gauge bosons in the Standard Model acquire mass via spontaneous symmetry breaking of the SU(2) gauge symmetry. The Minimal Supersymmetric Standard Model (MSSM) predicts several Higgs bosons. A new particle expected to be the Higgs boson was observed at the CERN/LHC on 14 March 2013, around the energy of 126.5 GeV with an accuracy of close to five sigma (99.9999%, which is accepted as definitive). The Higgs mechanism giving mass to other particles has not been observed.

Elementary bosons responsible for the four fundamental forces of nature are called force particles (gauge bosons). Strong interaction is mediated by the gluon, weak interaction is mediated by the W and Z bosons.

Name Symbol Antiparticle Charge (e) Spin Mass (GeV/c2) [5] Interaction mediated Observed
Graviton G Self 0 2 0 Gravitation No

The graviton, listed separately above, 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, below. 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.

Hypothetical particles

Supersymmetric theories predict the existence of more particles, none of which have been confirmed experimentally as of March 2019

Superpartners (Sparticles)
Superpartner Superpartner of Spin Notes
neutralino neutral bosons 12 The neutralinos are superpositions of the superpartners of neutral Standard Model bosons: neutral Higgs boson, Z boson and photon.
The lightest neutralino is a leading candidate for dark matter.
The MSSM predicts four neutralinos.
chargino charged bosons 12 The charginos are superpositions of the superpartners of charged Standard Model bosons: charged Higgs boson and W boson.
The MSSM predicts two pairs of charginos.
photino photon 12 Mixing with zino and neutral Higgsinos for neutralinos.
wino, zino W± and Z0 bosons 12 The charged wino mixing with the charged Higgsino for charginos, for the zino see line above.
Higgsino Higgs boson 0 For supersymmetry there is a need for several Higgs bosons, neutral and charged, according with their superpartners.
gluino gluon 12 Eight gluons and eight gluinos.
gravitino graviton 32 Predicted by supergravity (SUGRA). The graviton is hypothetical, too – see next table.
sleptons leptons 0 The superpartners of the leptons (electron, muon, tau) and the neutrinos.
sneutrino neutrino 0 Introduced by many extensions of the Standard Supermodel, and may be needed to explain the LSND results.
A special role has the sterile sneutrino, the supersymmetric counterpart of the hypothetical right-handed neutrino, called the "sterile neutrino".
squarks quarks 0 The stop squark (superpartner of the top quark) is thought to have a low mass and is often the subject of experimental searches.

Note: just as the photon, Z boson and W± bosons are superpositions of the B0, W0, W1, and W2 fields – the photino, zino, and wino± are superpositions of the bino0, wino0, wino1, and wino2 by definition.
No matter if one uses the original gauginos or this superpositions as a basis, the only predicted physical particles are neutralinos and charginos as a superposition of them together with the Higgsinos.

Other theories predict the existence of additional bosons:

Other hypothetical bosons and fermions
Name Spin Notes
dual graviton 2 Has been hypothesized as dual of graviton under electric-magnetic duality in supergravity.
graviscalar 0 Also known as "radion".
graviphoton 1 Also known as "gravivector".[6]
axion 0 A pseudoscalar particle introduced in Peccei–Quinn theory to solve the strong-CP problem.
axino 12 Superpartner of the axion. Forms, together with the saxion and axion, a supermultiplet in supersymmetric extensions of Peccei–Quinn theory.
saxion 0
branon ? Predicted in brane world models.
dilaton 0 Predicted in some string theories.
dilatino 12 Superpartner of the dilaton.
X and Y bosons 1 These leptoquarks are predicted by GUT theories to be heavier equivalents of the W and Z.
W' and Z' bosons 1
inflaton 0 Unknown force-carrier that is presumed to have the physical cause of cosmological “inflation” – the rapid expansion from 10−35 to 10−34 seconds after the Big Bang.
magnetic photon ? A. Salam (1966). "Magnetic monopole and two photon theories of C-violation." Physics Letters 22 (5): 683–684.
majoron 0 Predicted to understand neutrino masses by the seesaw mechanism.
majorana fermion 12 ; ​32 ?... gluino, neutralino, or other – is its own antiparticle.
chameleon 0 a possible candidate for dark energy and dark matter, and may contribute to cosmic inflation.

Mirror particles are predicted by theories that restore parity symmetry.

"Magnetic monopole" is a generic name for particles with non-zero magnetic charge. They are predicted by some GUTs.

"Tachyon" is a generic name for hypothetical particles that travel faster than the speed of light (and so paradoxically experience time in reverse due to inversal of Theory of relativity) and have an imaginary rest mass, they would violate the laws of causality.

Preons were suggested as subparticles of quarks and leptons, but modern collider experiments have all but ruled out their existence.

Kaluza–Klein towers of particles are predicted by some models of extra dimensions. The extra-dimensional momentum is manifested as extra mass in four-dimensional spacetime.

Composite particles

Hadrons

Hadrons are defined as strongly interacting composite particles. Hadrons are either:

  • Composite fermions (especially 3 quarks), in which case they are called baryons.
  • Composite bosons (especially 2 quarks), in which case they are called mesons.

Quark models, first proposed in 1964 independently by Murray Gell-Mann and George Zweig (who called quarks "aces"), describe the known hadrons as composed of valence quarks and/or antiquarks, tightly bound by the color force, which is mediated by gluons. A "sea" of virtual quark-antiquark pairs is also present in each hadron.

Baryons

Baryon decuplet
A combination of three u, d or s-quarks with a total spin of ​32 form the so-called "baryon decuplet".
Proton quark structure
Proton quark structure: 2 up quarks and 1 down quark. The gluon tubes or flux tubes are now known to be Y shaped.

Ordinary baryons (composite fermions) contain three valence quarks or three valence antiquarks each.

  • Nucleons are the fermionic constituents of normal atomic nuclei:
    • Protons, composed of two up and one down quark (uud)
    • Neutrons, composed of two down and one up quark (ddu)
  • Hyperons, such as the Λ, Σ, Ξ, and Ω particles, which contain one or more strange quarks, are short-lived and heavier than nucleons. Although not normally present in atomic nuclei, they can appear in short-lived hypernuclei.
  • A number of charmed and bottom baryons have also been observed.
  • Pentaquarks consist of four valence quarks and one valence antiquark.
  • Other exotic baryons may also exist.

Mesons

Noneto mesônico de spin 0
Mesons of spin 0 form a nonet

Ordinary mesons are made up of a valence quark and a valence antiquark. Because mesons have spin of 0 or 1 and are not themselves elementary particles, they are "composite" bosons. 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

Helium atom QM
A semi-accurate depiction of the helium atom. In the nucleus, the protons are in red and neutrons are in purple. In reality, the nucleus is also spherically symmetrical.

Atomic nuclei consist of protons and neutrons. Each type of nucleus contains a specific number of protons and a specific number of neutrons, and is called a "nuclide" or "isotope". Nuclear reactions can change one nuclide into another. See table of nuclides for a complete list of isotopes.

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. Each type of atom corresponds to a specific chemical element. To date, 118 elements have been discovered or created.

The atomic nucleus consists of protons and neutrons. Protons and neutrons are, in turn, made of quarks.

Molecules

Molecules are the smallest particles into which a non-elemental substance can be divided while maintaining the physical properties of the substance. Each type of molecule corresponds to a specific chemical compound. Molecules are a composite of two or more atoms. See list of compounds for a list of molecules. A molecule is generally combined in a fixed proportion. It is the most basic unit of matter and is homogenous.

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:

Other

  • Accelerons are hypothetical particles postulated to relate neutrino mass to dark energy, and are named for the role they play in the accelerating expansion of the universe
  • An anyon is a generalization of fermion and boson in two-dimensional systems like sheets of graphene that obeys braid statistics.
  • A plekton is a theoretical kind of particle discussed as a generalization of the braid statistics of the anyon to dimension > 2.
  • A WIMP (weakly interacting massive particle) is any one of a number of particles that might explain dark matter (such as the neutralino or the axion).
  • A GIMP (gravitationally interacting massive particle) is a particle which provides an alternative explanation of dark matter, instead of the aforementioned WIMP.
  • The pomeron, used to explain the elastic scattering of hadrons and the location of Regge poles in Regge theory.
  • The skyrmion, a topological solution of the pion field, used to model the low-energy properties of the nucleon, such as the axial vector current coupling and the mass.
  • A genon is a particle existing in a closed timelike world line where spacetime is curled as in a Frank Tipler or Ronald Mallett time machine.
  • A goldstone boson is 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.
  • A goldstino is a goldstone fermion produced by the spontaneous breaking of supersymmetry.
  • An instanton is a field configuration which is a local minimum of the Euclidean action. Instantons are used in nonperturbative calculations of tunneling rates.
  • A dyon is a hypothetical particle with both electric and magnetic charges.
  • A geon is an electromagnetic or gravitational wave which is held together in a confined region by the gravitational attraction of its own field of energy.
  • An inflaton is the generic name for an unidentified scalar particle responsible for the cosmic inflation.
  • A spurion is the name given to a "particle" inserted mathematically into an isospin-violating decay in order to analyze it as though it conserved isospin.
  • What is called "true muonium", a bound state of a muon and an antimuon, is a theoretical exotic atom which has never been observed.
  • An ion (a charged atom or molecule) is either an anion or a cation.
  • A dislon is a localized collective excitation of a crystal dislocation around the static displacement.

Classification by speed

  • A tardyon or bradyon travels slower than light and has a non-zero rest mass.
  • A luxon travels at the speed of light and has no rest mass.
  • A tachyon (mentioned above) is a hypothetical particle that travels faster than the speed of light and has an imaginary rest mass.

See also

References

  1. ^ Sylvie Braibant; Giorgio Giacomelli; Maurizio Spurio (2012). Particles and Fundamental Interactions: An Introduction to Particle Physics (1st ed.). Springer. p. 1. ISBN 978-94-007-2463-1.
  2. ^ Khachatryan, V.; et al. (CMS Collaboration) (2012). "Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC". Physics Letters B. 716 (2012): 30–61. arXiv:1207.7235. Bibcode:2012PhLB..716...30C. doi:10.1016/j.physletb.2012.08.021.
  3. ^ Abajyan, T.; et al. (ATLAS Collaboration) (2012). "Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC". Physics Letters B. 716 (2012): 1–29. arXiv:1207.7214. Bibcode:2012PhLB..716....1A. doi:10.1016/j.physletb.2012.08.020.
  4. ^ Kayser, Boris (2010). "Two Questions About Neutrinos". arXiv:1012.4469 [hep-ph].
  5. ^ a b c d Particle Data Group (2016). "Review of Particle Physics". Chinese Physics C. 40 (10): 100001. Bibcode:2016ChPhC..40j0001P. doi:10.1088/1674-1137/40/10/100001. hdl:1983/c6dc3926-daee-4d0e-9149-5ff3a8120574.
  6. ^ Maartens, R. (2004). "Brane-World Gravity" (PDF). Living Reviews in Relativity. 7 (1): 7. arXiv:gr-qc/0312059. Bibcode:2004LRR.....7....7M. doi:10.12942/lrr-2004-7. PMC 5255527. PMID 28163642.
Antineutron

The antineutron is the antiparticle of the neutron with symbol n. It differs from the neutron only in that some of its properties have equal magnitude but opposite sign. It has the same mass as the neutron, and no net electric charge, but has opposite baryon number (+1 for neutron, −1 for the antineutron). This is because the antineutron is composed of antiquarks, while neutrons are composed of quarks. The antineutron consists of one up antiquark and two down antiquarks.

Since the antineutron is electrically neutral, it cannot easily be observed directly. Instead, the products of its annihilation with ordinary matter are observed. In theory, a free antineutron should decay into an antiproton, a positron and a neutrino in a process analogous to the beta decay of free neutrons. There are theoretical proposals of neutron–antineutron oscillations, a process that implies the violation of the baryon number conservation.The antineutron was discovered in proton–antiproton collisions at the Bevatron (Lawrence Berkeley National Laboratory) by Bruce Cork in 1956, one year after the antiproton was discovered.

Chemical species

A chemical species is a chemical substance or ensemble composed of chemically identical molecular entities that can explore the same set of molecular energy levels on a characteristic or delineated time scale. The term is applied equally to a set of chemically identical atomic or molecular structural units in a solid array.In supramolecular chemistry, chemical species are those supramolecular structures whose interactions and associations are brought about via intermolecular bonding and debonding actions, and function to form the basis of this branch of chemistry.

Chronon

A chronon is a proposed quantum of time, that is, a discrete and indivisible "unit" of time as part of a hypothesis that proposes that time is not continuous.

D meson

The D mesons are the lightest particle containing charm quarks. They are often studied to gain knowledge on the weak interaction. The strange D mesons (Ds) were called the "F mesons" prior to 1986.

Delta ray

A delta ray is a secondary electron with enough energy to escape a significant distance away from the primary radiation beam and produce further ionization", and is sometimes used to describe any recoil particle caused by secondary ionization. The term was coined by J. J. Thomson.

Hadron

In particle physics, a hadron (listen) (Greek: ἁδρός, hadrós; "stout, thick") is a composite particle made of two or more quarks held together by the strong force in a similar way as molecules are held together by the electromagnetic force. Most of the mass of ordinary matter comes from two hadrons, the proton and the neutron.

Hadrons are categorized into two families: baryons, made of an odd number of quarks – usually three quarks – and mesons, made of an even number of quarks—usually one quark and one antiquark. Protons and neutrons are examples of baryons; pions are an example of a meson. "Exotic" hadrons, containing more than three valence quarks, have been discovered in recent years. A tetraquark state (an exotic meson), named the Z(4430)−, was discovered in 2007 by the Belle Collaboration and confirmed as a resonance in 2014 by the LHCb collaboration. Two pentaquark states (exotic baryons), named P+c(4380) and P+c(4450), were discovered in 2015 by the LHCb collaboration. There are several more exotic hadron candidates, and other colour-singlet quark combinations that may also exist.

Almost all "free" hadrons and antihadrons (meaning, in isolation and not bound within an atomic nucleus) are believed to be unstable and eventually decay (break down) into other particles. The only known exception relates to free protons, which are possibly stable, or at least, take immense amounts of time to decay (order of 1034+ years). Free neutrons are unstable and decay with a half-life of about 611 seconds. Their respective antiparticles are expected to follow the same pattern, but they are difficult to capture and study, because they immediately annihilate on contact with ordinary matter. "Bound" protons and neutrons, contained within an atomic nucleus, are generally considered stable. Experimentally, hadron physics is studied by colliding protons or nuclei of heavy elements such as lead or gold, and detecting the debris in the produced particle showers. In the environment, mesons such as pions are produced by the collisions of cosmic rays with the atmosphere.

Hyperon

In particle physics, a hyperon is any baryon containing one or more strange quarks, but no charm, bottom, or top quark. This form of matter may exist in a stable form within the core of some neutron stars.

Japanese particles

Japanese particles, joshi (助詞) or tenioha (てにをは), are suffixes or short words in Japanese grammar that immediately follow the modified noun, verb, adjective, or sentence. Their grammatical range can indicate various meanings and functions, such as speaker affect and assertiveness.

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 composed of one quark and one antiquark. They are part of the hadron particle family – particles made of quarks. The other members of the hadron family are the baryons – subatomic particles composed of three quarks. The main difference between mesons and baryons is that mesons have integer spin (thus are bosons) while baryons are fermions (half-integer spin). Because mesons are bosons, the Pauli exclusion principle does not apply to them. Because of this, they can act as force mediating particles on short distances, and thus play a part in processes such as the nuclear interaction.

Since mesons are composed of quarks, they participate in both the weak and strong interactions. Mesons with net electric charge also participate in the electromagnetic interaction. They are classified according to their quark content, total angular momentum, parity, and various other properties such as C-parity and G-parity. While no meson is stable, those of lower mass are nonetheless more stable than the most massive mesons, and are easier to observe and study in particle accelerators or in cosmic ray experiments. They are also typically less massive than baryons, meaning that they are more easily produced in experiments, and will exhibit higher-energy phenomena sooner than baryons would. For example, the charm quark was first seen in the J/Psi meson (J/ψ) in 1974, and the bottom quark in the upsilon meson (ϒ) in 1977.Each meson has a corresponding antiparticle (antimeson) where quarks are replaced by their corresponding antiquarks and vice versa. For example, a positive pion (π+) is made of one up quark and one down antiquark; and its corresponding antiparticle, the negative pion (π−), is made of one up antiquark and one down quark. Some experiments show the evidence of tetraquarks – "exotic" mesons made of two quarks and two antiquarks, but the particle physics community as a whole does not view their existence as likely, although still possible.The symbols encountered in these lists are: I (isospin), J (total angular momentum), P (parity), C (C-parity), G (G-parity), u (up quark), d (down quark), s (strange quark), c (charm quark), b (bottom quark), Q (charge), B (baryon number), S (strangeness), C (charm), and B′ (bottomness), as well as a wide array of subatomic particles (hover for name).

Neutron capture

Neutron capture is a nuclear reaction in which an atomic nucleus and one or more neutrons collide and merge to form a heavier nucleus. Since neutrons have no electric charge, they can enter a nucleus more easily than positively charged protons, which are repelled electrostatically.Neutron capture plays an important role in the cosmic nucleosynthesis of heavy elements. In stars it can proceed in two ways: as a rapid (r-process) or a slow process (s-process). Nuclei of masses greater than 56 cannot be formed by thermonuclear reactions (i.e. by nuclear fusion), but can be formed by neutron capture.

Neutron capture on protons yields a line at 2.223 MeV predicted and commonly observed in solar flares.

Outline of nuclear technology

The following outline is provided as an overview of and topical guide to nuclear technology:

Nuclear technology – involves the reactions of atomic nuclei. Among the notable nuclear technologies are nuclear power, nuclear medicine, and nuclear weapons. It has found applications from smoke detectors to nuclear reactors, and from gun sights to nuclear weapons.

Particle

In the physical sciences, a particle (or corpuscule in older texts) is a small localized object to which can be ascribed several physical or chemical properties such as volume, density or mass. They vary greatly in size or quantity, from subatomic particles like the electron, to microscopic particles like atoms and molecules, to macroscopic particles like powders and other granular materials. Particles can also be used to create scientific models of even larger objects depending on their density, such as humans moving in a crowd or celestial bodies in motion.

The term 'particle' is rather general in meaning, and is refined as needed by various scientific fields. Something that is composed of particles may be referred to as being particulate. However, the noun 'particulate' is most frequently used to refer to pollutants in the Earth's atmosphere, which are a suspension of unconnected particles, rather than a connected particle aggregation.

Particle detector

In experimental and applied particle physics, nuclear physics, and nuclear engineering, a particle detector, also known as a radiation detector, is a device used to detect, track, and/or identify ionizing particles, such as those produced by nuclear decay, cosmic radiation, or reactions in a particle accelerator. Detectors can measure the particle energy and other attributes such as momentum, spin, charge, particle type, in addition to merely registering the presence of the particle.

Particle zoo

In particle physics, the term particle zoo is used colloquially to describe a relatively extensive list of the then known "elementary particles" by comparison to the variety of species in a zoo.

In the history of particle physics, the situation was particularly confusing in the late 1960s. Before the discovery of quarks, hundreds of strongly interacting particles (hadrons) were known and believed to be distinct elementary particles in their own right. It was later discovered that they were not elementary particles, but rather composites of the quarks. The set of particles believed today to be elementary is known as the Standard Model and includes quarks, bosons and leptons.

Phi meson

In particle physics, the phi meson or ϕ meson is a vector meson formed of a strange quark and a strange antiquark. It was the ϕ meson's unusual propensity to decay into K0 and K0 that led to the discovery of the OZI rule. It has a mass of 1019.461±0.020 MeV/c2 and a mean lifetime of 1.55±0.01 × 10−22s.

Positron

The positron or antielectron is the antiparticle or the antimatter counterpart of the electron. The positron has an electric charge of +1 e, a spin of 1/2 (same as electron), and has the same mass as an electron. When a positron collides with an electron, annihilation occurs. If this collision occurs at low energies, it results in the production of two or more gamma ray photons.

Positrons can be created by positron emission radioactive decay (through weak interactions), or by pair production from a sufficiently energetic photon which is interacting with an atom in a material.

Proton capture

Proton capture is a nuclear reaction in which an atomic nucleus and one or more protons collide and merge to form a heavier nucleus.

Since protons have positive electric charge, they are repelled electrostatically by the positively charged nucleus. Therefore, it is more difficult for protons to enter the nucleus compared to neutrally charged neutrons .

Proton capture plays an important role in the cosmic nucleosynthesis of proton rich isotopes. In stars it can proceed in two ways: as a rapid (rp-process) or a slow process (p-process).

Subatomic particle

In the physical sciences, subatomic particles are particles much smaller than atoms. The two types of subatomic particles are: elementary particles, which according to current theories are not made of other particles; and composite particles. Particle physics and nuclear physics study these particles and how they interact.

The idea of a particle underwent serious rethinking when experiments showed that light could behave like a stream of particles (called photons) as well as exhibiting wave-like properties. This led to the new concept of wave–particle duality to reflect that quantum-scale "particles" behave like both particles and waves (they are sometimes described as wavicles to reflect this). Another new concept, the uncertainty principle, states that some of their properties taken together, such as their simultaneous position and momentum, cannot be measured exactly. In more recent times, wave–particle duality has been shown to apply not only to photons but to increasingly massive particles as well.Interactions of particles in the framework of quantum field theory are understood as creation and annihilation of quanta of corresponding fundamental interactions. This blends particle physics with field theory.

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