View source for Subatomic particle

{{Short description|Particle smaller than an atom}}
[[File:Quark structure proton.svg|thumb|upright=0.8|A composite particle [[proton]] is made of two [[up quark]]s and one [[down quark]], which are [[elementary particle]]s.]]

In [[physics]], a '''subatomic particle''' is a [[particle]] smaller than an [[atom]].<ref>{{cite web|title=Subatomic particles|url=http://www.ndt-ed.org/EducationResources/HighSchool/Radiography/subatomicparticles.htm|publisher=NTD|access-date=5 June 2012|archive-date=16 February 2014|archive-url=https://web.archive.org/web/20140216092512/http://www.ndt-ed.org/EducationResources/HighSchool/Radiography/subatomicparticles.htm|url-status=dead}}</ref> According to the [[Standard Model|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 a [[proton]] or a [[neutron]], composed of three [[quarks]]; or a [[meson]], composed of two [[quark]]s), or an [[elementary particle]], which is not composed of other particles (for example, quarks; or [[electrons]], [[muons]], and [[Tau (particle)|tau]] particles, which are called [[leptons]]).<ref>{{cite book|last=Bolonkin|first=Alexander|title=Universe, Human Immortality and Future Human Evaluation|date=2011|publisher=[[Elsevier]]|isbn=9780124158016|pages=25}}</ref> [[Particle physics]] and [[nuclear physics]] study these particles and how they interact.<ref>
{{cite book
 | last = Fritzsch  | first = Harald
 | date = 2005
 | title = Elementary Particles
 | url = https://archive.org/details/elementarypartic0000frit
 | url-access = registration  | pages = [https://archive.org/details/elementarypartic0000frit/page/11 11]–20
 | publisher = [[World Scientific]]
 | isbn = 978-981-256-141-1
}}</ref> Most force-carrying particles like [[photons]] or [[gluons]] are called [[bosons]] and, although they have quanta of energy, do not have rest mass or discrete diameters (other than pure energy wavelength) and are unlike the former particles that have rest mass and cannot overlap or combine which are called [[fermions]]. The [[W and Z bosons]], however, are an exception to this rule and have relatively large rest masses at approximately {{val|80|ul=GeV/c2}} and {{val|90|u=GeV/c2}} respectively.

Experiments show that light could behave like a [[stream of particles]] (called [[photon]]s) as well as exhibiting wave-like properties. This led to the concept of [[wave–particle duality]] to reflect that quantum-scale {{em|particles}} behave both like particles and like [[wave]]s; they are occasionally called ''wavicles'' to reflect this.<ref>{{cite book|url=https://doi.org/10.1007/978-1-4684-5386-7_18|title=Quantum Uncertainties: Recent and Future Experiments and Interpretations|first1=Geoffrey|last1=Hunter|first2=Robert L. P.|last2=Wadlinger|editor-first1=William M.|editor-last1=Honig|editor-first2=David W.|editor-last2=Kraft|editor-first3=Emilio|editor-last3=Panarella|date=August 23, 1987|publisher=Springer US|pages=331–343|via=Springer Link|doi=10.1007/978-1-4684-5386-7_18 |quote=The finite-field model of the photon is both a particle and a wave, and hence we refer to it by Eddington's name "wavicle". }}</ref>

Another concept, the [[uncertainty principle]], states that some of their properties taken together, such as their simultaneous [[position (vector)|position]] and [[momentum]], cannot be measured exactly.<ref>{{cite journal |last=Heisenberg |first=W. |date=1927 |title=Über den anschaulichen Inhalt der quantentheoretischen Kinematik und Mechanik |journal=[[Zeitschrift für Physik]] |language=de |volume=43 |issue=3–4 |pages=172–198 |bibcode=1927ZPhy...43..172H |doi=10.1007/BF01397280 |s2cid=122763326 }}</ref> 
Interactions of particles in the framework of [[quantum field theory]] are understood as creation and annihilation of ''[[quantum|quanta]]'' of corresponding [[fundamental interaction]]s. This blends particle physics with [[Quantum field theory|field theory]].

Even among [[particle physics|particle physicists]], the exact definition of a particle has diverse descriptions. These professional attempts at the definition of a particle include:<ref>{{cite web |date=12 November 2020 |title=What is a Particle? |url=https://www.quantamagazine.org/what-is-a-particle-20201112/}}</ref>  
* A particle is a [[wave function collapse|collapsed wave function]]
* A particle is an excitation of a [[Quantum field theory|quantum field]]
* A particle is an [[Poincaré group|irreducible representation of the Poincaré group]]
* A particle is an observed thing

{| class="wikitable"
|+ Particles in the atom
! Subatomic particle !! Symbol !! Type !! Location in atom !! Charge{{br}}{{bracket|''[[Elementary charge|e]]''}} !! Mass{{br}}{{bracket|[[Dalton (unit)|Da]]}}
|-
| proton || p<sup>+</sup> || composite || nucleus || +1 || ≈ 1
|-
| neutron || n<sup>0</sup> || composite || nucleus || 0 || ≈ 1
|-
| electron || e<sup>−</sup> || elementary || shells || −1 || ≈ {{sfrac|1|2000}}
|}

== Classification ==

=== By composition ===
Subatomic particles are either "elementary", i.e. not made of multiple other particles, or "composite" and made of more than one elementary particle bound together. 
 
The elementary particles of the [[Standard Model]] are:<ref name="IntroSM1">
{{cite book |last1=Cottingham |first1=W. N. |url=https://books.google.com/books?id=Dm36BYq9iu0C |title=An introduction to the standard model of particle physics |last2=Greenwood |first2=D.A. |date=2007 |publisher=[[Cambridge University Press]] |isbn=978-0-521-85249-4 |page=1}}</ref>
* Six "[[Flavour (particle physics)|flavors]]" of [[quark]]s: [[Up quark|up]], [[Down quark|down]], [[Strange quark|strange]], [[Charm quark|charm]], [[Bottom quark|bottom]], and [[Top quark|top]];
* Six types of [[lepton]]s: [[electron]], [[electron neutrino]], [[muon]], [[muon neutrino]], [[tau (particle)|tau]], [[tau neutrino]];
* Twelve [[gauge boson]]s (force carriers): the photon of [[electromagnetism]], the three W and Z bosons of the [[weak interaction|weak force]], and the eight gluons of the [[strong force]];
* The [[Higgs boson]].
[[File:Standard Model of Elementary Particles.svg|thumb|upright=1.8|The [[Standard Model]] classification of elementary particles]]

All of these have now been discovered through experiments, with the latest being the top quark (1995), tau neutrino (2000), and Higgs boson (2012).

Various [[Physics beyond the Standard Model|extensions of the Standard Model]] predict the existence of an elementary [[graviton]] particle and [[List of elementary particles#Hypothetical particles|many other elementary particles]], but none have been discovered as of 2021.

==== Hadrons ====
The word hadron comes from Greek and was introduced in 1962 by [[Lev Okun]].<ref>{{cite conference |first=Lev |last=Okun |author-link=Lev Okun |year=1962 |title=The theory of weak interaction |conference=International Conference on High-Energy Physics |place=CERN, Geneva, CH |book-title=Proceedings of 1962 International Conference on High-Energy Physics at CERN |page=845 |type=plenary talk |bibcode=1962hep..conf..845O}}</ref> Nearly all composite particles contain multiple quarks (and/or antiquarks) bound together by gluons (with a few exceptions with no quarks, such as [[positronium]] and [[muonium]]). Those containing few (≤&nbsp;5) quarks (including antiquarks) are called [[hadron]]s. Due to a property known as [[color confinement]], quarks are never found singly but always occur in hadrons containing multiple quarks. The hadrons are divided by number of quarks (including antiquarks) into the [[baryons]] containing an odd number of quarks (almost always 3), of which the [[proton]] and [[neutron]] (the two [[nucleons]]) are by far the best known; and the [[meson]]s containing an even number of quarks (almost always 2, one quark and one antiquark), of which the [[pion]]s and [[kaon]]s are the best known.

Except for the proton and neutron, all other hadrons are unstable and decay into other particles in microseconds or less. A proton is made of two [[up quark]]s and one [[down quark]], while the neutron is made of two down quarks and one up quark. These commonly bind together into an atomic nucleus, e.g. a helium-4 nucleus is composed of two protons and two neutrons. Most hadrons do not live long enough to bind into nucleus-like composites; those that do (other than the proton and neutron) form [[exotic nuclei]].

=== By statistics ===
{{main|Spin–statistics theorem}}
[[File:Bosons-Hadrons-Fermions-RGB.svg|thumb|upright=1.6|Overlap between [[boson]]s, [[hadron]]s, and [[fermion]]s]]
Any subatomic particle, like any particle in the [[three-dimensional space]] that obeys the [[Scientific law|laws]] of [[quantum mechanics]], can be either a boson (with integer [[Spin (physics)|spin]]) or a fermion (with odd half-integer spin).

In the Standard Model, all the elementary fermions have spin 1/2, and are divided into the quarks which carry [[color charge]] and therefore feel the strong interaction, and the [[leptons]] which do not. The elementary bosons comprise the gauge bosons (photon, W and Z, gluons) with spin 1, while the Higgs boson is the only elementary particle with spin zero.

The hypothetical graviton is required theoretically to have spin 2, but is not part of the Standard Model. Some extensions such as [[supersymmetry]] predict additional elementary particles with spin 3/2, but none have been discovered as of 2023.

Due to the laws for spin of composite particles, the baryons (3 quarks) have spin either 1/2 or 3/2 and are therefore fermions; the mesons (2 quarks) have integer spin of either 0 or 1 and are therefore bosons.

=== By mass ===
In [[special relativity]], the [[Mass–energy equivalence|energy of a particle at rest equals its mass times the speed of light squared]], {{nowrap begin}}''E'' = ''mc''<sup>2</sup>{{nowrap end}}. That is, [[mass]] can be expressed in terms of [[energy]] and vice versa. If a particle has a [[frame of reference]] in which it lies [[rest (physics)|at rest]], then it has a positive [[rest mass]] and is referred to as ''massive''.

All composite particles are massive. Baryons (meaning "heavy") tend to have greater mass than mesons (meaning "intermediate"), which in turn tend to be heavier than leptons (meaning "lightweight"), but the heaviest lepton (the [[tau particle]]) is heavier than the two lightest flavours of baryons ([[nucleon]]s). It is also certain that any particle with an [[electric charge]] is massive.

When originally defined in the 1950s, the terms baryons, mesons and leptons referred to masses; however, after the quark model became accepted in the 1970s, it was recognised that baryons are composites of three quarks, mesons are composites of one quark and one antiquark, while leptons are elementary and are defined as the elementary fermions with no color charge.

All [[massless particle]]s (particles whose [[invariant mass]] is zero) are elementary. These include the photon and gluon, although the latter cannot be isolated.

=== By decay ===
Most subatomic particles are not stable. All leptons, as well as baryons [[particle decay|decay]] by either the strong force or weak force (except for the proton). Protons are not known to [[Proton decay|decay]], although whether they are "truly" stable is unknown, as some very important Grand Unified Theories (GUTs) actually require it. The μ and τ muons, as well as their antiparticles, decay by the weak force. Neutrinos (and antineutrinos) do not decay, but a related phenomenon of [[neutrino oscillation]]s is thought to exist even in vacuums. The electron and its antiparticle, the [[positron]], are theoretically stable due to [[charge conservation]] unless a lighter particle having [[absolute value|magnitude]] of electric charge {{abbr|≤|less than or equal}}&nbsp;[[elementary charge|''e'']] exists (which is unlikely). Its charge is not shown yet.

== Other properties ==
All observable subatomic particles have their electric charge an [[integer]] multiple of the [[elementary charge]]. The Standard Model's quarks have "non-integer" electric charges, namely, multiple of {{sfrac|1|3}}&nbsp;''e'', but quarks (and other combinations with non-integer electric charge) cannot be isolated due to [[color confinement]]. For baryons, mesons, and their antiparticles the constituent quarks' charges sum up to an integer multiple of ''e''.

Through the work of [[Albert Einstein]], [[Satyendra Nath Bose]], [[Louis de Broglie]], and many others, current scientific theory holds that ''all'' particles also have a wave nature.<ref>
{{cite book
 | first = Walter
 | last = Greiner
 | date = 2001
 | title = Quantum Mechanics: An Introduction
 | url = https://books.google.com/books?id=7qCMUfwoQcAC&pg=PA29
 | page = 29
 | publisher = [[Springer (publisher)|Springer]]
 | isbn = 978-3-540-67458-0
}}</ref> This has been verified not only for elementary particles but also for compound particles like atoms and even molecules. In fact, according to traditional formulations of non-relativistic quantum mechanics, wave–particle duality applies to all objects, even macroscopic ones; although the wave properties of macroscopic objects cannot be detected due to their small wavelengths.<ref>
{{cite book
 |author=Eisberg, R.
 |author2=Resnick, R.
 |name-list-style=amp
 |date=1985
 |title=Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles
 |publisher=[[John Wiley & Sons]]
 |edition=2nd
 |pages=[https://archive.org/details/quantumphysicsof00eisb/page/59 59–60]
 |isbn=978-0-471-87373-0
 |quote=For both large and small wavelengths, both matter and radiation have both particle and wave aspects. [...] But the wave aspects of their motion become more difficult to observe as their wavelengths become shorter. [...] For ordinary macroscopic particles the mass is so large that the momentum is always sufficiently large to make the de Broglie wavelength small enough to be beyond the range of experimental detection, and classical mechanics reigns supreme.
 |url=https://archive.org/details/quantumphysicsof00eisb/page/59
}}</ref>

Interactions between particles have been scrutinized for many centuries, and a few simple laws underpin how particles behave in collisions and interactions. The most fundamental of these are the laws of [[conservation of energy]] and [[conservation of momentum]], which let us make calculations of particle interactions on scales of magnitude that range from stars to quarks.<ref>{{cite book |last=Newton |first=Isaac |title=The Mathematical Principles of Natural Philosophy |title-link=Philosophiæ Naturalis Principia Mathematica |year=1687 |location=England |chapter=Axioms or Laws of Motion}}</ref> These are the prerequisite basics of [[Newtonian mechanics]], a series of statements and equations in ''[[Philosophiae Naturalis Principia Mathematica]]'', originally published in 1687.

== Dividing an atom ==
The negatively charged electron has a mass of about {{sfrac|1836}} of that of a [[hydrogen]] atom. The remainder of the hydrogen atom's mass comes from the positively charged [[proton]]. The [[atomic number]] of an element is the number of protons in its nucleus. Neutrons are neutral particles having a mass slightly greater than that of the proton. Different [[isotope]]s of the same element contain the same number of protons but different numbers of neutrons. The [[mass number]] of an isotope is the total number of [[nucleon]]s (neutrons and protons collectively).

[[Chemistry]] concerns itself with how electron sharing binds atoms into structures such as crystals and [[molecule]]s. The subatomic particles considered important in the understanding of chemistry are the [[electron]], the [[proton]], and the [[neutron]]. [[Nuclear physics]] deals with how protons and neutrons arrange themselves in nuclei. The study of subatomic particles, atoms and molecules, and their structure and interactions, requires [[quantum mechanics]]. Analyzing processes that change the numbers and types of particles requires [[quantum field theory]]. The study of subatomic particles ''per se'' is called [[particle physics]]. The term ''[[high-energy physics]]'' is nearly synonymous to "particle physics" since creation of particles requires high energies: it occurs only as a result of [[cosmic ray]]s, or in [[particle accelerator]]s. [[phenomenology (particle physics)|Particle phenomenology]] systematizes the knowledge about subatomic particles obtained from these experiments.<ref>{{cite book |last=Taiebyzadeh |first=Payam |title=String Theory: A Unified Theory and Inner Dimension Of Elementary Particles (Baz Dahm) |publisher=Shamloo Publications |year=2017 |isbn=978-6-00-116684-6 |location=Iran}}</ref>

== History ==
{{main|History of subatomic physics|Timeline of particle discoveries}}
The term "''subatomic'' particle" is largely a [[retronym]] of the 1960s, used to distinguish a large number of [[baryon]]s and [[meson]]s (which comprise [[hadron]]s) from particles that are now thought to be [[elementary particle|truly elementary]]. Before that hadrons were usually classified as "elementary" because their composition was unknown.{{Primary sources|section|date=March 2025}}

A list of important discoveries follows:
{| class="wikitable"
 !Particle
 !Composition
 !Theorized
 !Discovered
 !Comments
 |-
 |[[electron]] {{subatomic particle|electron}}
 |elementary ([[lepton]])
 |[[G. Johnstone Stoney]] (1874)<ref>
  {{cite journal
   |last=Stoney |first=G. Johnstone
   |date=1881 |title=LII. On the physical units of nature
   |url=https://www.tandfonline.com/doi/full/10.1080/14786448108627031
   |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science
   |language=en |volume=11 |issue=69 |pages=381–390 |doi=10.1080/14786448108627031 |issn=1941-5982
  |url-access=subscription }}</ref>
 |[[J. J. Thomson]] (1897)<ref name="referenceB">
  {{cite journal |last=Thomson |first=J. J. |year=1897 |title=Cathode Rays |url=https://books.google.com/books?id=vBZbAAAAYAAJ&pg=PA104 |journal=The Electrician |volume=39 |page=104}}</ref>
 |Minimum unit of electrical charge, for which Stoney suggested the name in 1891.<ref>
  {{cite journal
   |last=Klemperer |first=Otto |author1-link=Otto Ernst Heinrich Klemperer
   |date=1959
   |title=Electron physics: The physics of the free electron
   |journal=Physics Today |volume=13 |issue=6 |pages=64–66
   |bibcode=1960PhT....13R..64K |doi=10.1063/1.3057011
  }}</ref> First subatomic particle to be identified.<ref>
  {{cite magazine
   |last=Alfred |first=Randy
   |title=April 30, 1897: J.J. Thomson Announces the Electron ... Sort Of
   |date=April 30, 2012
   |magazine=Wired
   |url=https://www.wired.com/2012/04/april-30-1897-j-j-thomson-announces-the-electron-sort-of/
   |access-date=2022-08-22 |issn=1059-1028
  }}</ref>
 |-
 |[[alpha particle]] {{subatomic particle|alpha}}
 |composite (atomic nucleus)
 |{{no|''never''}}
 |[[Ernest Rutherford]] (1899)<ref name="Rutherford-1899">
  {{cite journal
   |last=Rutherford |first=E.
   |date=1899
   |title=VIII. Uranium radiation and the electrical conduction produced by it
   |url=https://www.tandfonline.com/doi/full/10.1080/14786449908621245
   |journal=The London, Edinburgh, and Dublin Philosophical Magazine and Journal of Science
   |language=en |volume=47 |issue=284 |pages=109–163
   |doi=10.1080/14786449908621245 |issn=1941-5982
  |url-access=subscription}}</ref>
 |Proven by Rutherford and [[Thomas Royds]] in 1907 to be helium nuclei. Rutherford won the Nobel Prize for Chemistry in 1908 for this discovery.<ref>
  {{cite web |title=The Nobel Prize in Chemistry 1908
   |url=https://www.nobelprize.org/prizes/chemistry/1908/rutherford/facts/
   |access-date=2022-08-22
   |website=NobelPrize.org
   |language=en-US
  }}</ref>
 |-
 |[[photon]] {{subatomic particle|photon}}
 |elementary ([[quantum]])
 |[[Max Planck]] (1900)<ref>
  {{cite journal
   |last=Klein |first=Martin J.
   |date=1961
   |title=Max Planck and the beginnings of the quantum theory
   |url=http://link.springer.com/10.1007/BF00327765
   |journal=Archive for History of Exact Sciences
   |language=en |volume=1 |issue=5 |pages=459–479
   |doi=10.1007/BF00327765 |s2cid=121189755 |issn=0003-9519
  |url-access=subscription}}</ref>
 |[[Albert Einstein]] (1905)<ref>
  {{cite journal |last=Einstein |first=Albert |date=1905 |title=Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt |journal=Annalen der Physik |language=de |volume=322 |issue=6 |pages=132–148 |bibcode=1905AnP...322..132E |doi=10.1002/andp.19053220607 |doi-access=free}}</ref>
 |Necessary to solve the [[thermodynamics|thermodynamic]] problem of [[black-body radiation]].
 |-
 |[[proton]] {{subatomic particle|proton}}
 |composite ([[baryon]])
 |William Prout (1815)<ref name=lederman>{{cite book|last=Lederman|first=Leon|title=The God Particle|url=https://archive.org/details/godparticle00leon|url-access=registration|year=1993|publisher=Delta |isbn=9780385312110 |author-link=Leon Lederman}}</ref>
 |Ernest Rutherford (1919, named 1920)<ref>{{cite journal |last=Rutherford |first=Ernest |date=1920 |title=The Stability of Atoms |url=https://iopscience.iop.org/article/10.1088/1478-7814/33/1/337 |journal=Proceedings of the Physical Society of London |volume=33 |issue=1 |pages=389–394 |bibcode=1920PPSL...33..389R |doi=10.1088/1478-7814/33/1/337 |issn=1478-7814}}</ref><ref name="protonDebate" />
 |The nucleus of {{SimpleNuclide|hydrogen|1|link=yes}}.
 |-
 |[[neutron]] {{subatomic particle|neutron}}
 |composite (baryon)
 |Ernest Rutherford ({{circa}}1920<ref>{{cite journal |last1=Rutherford |first1=Ernest |date=1920 |title=Bakerian Lecture: Nuclear constitution of atoms |journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character |language=en |volume=97 |issue=686 |pages=374–400 |bibcode=1920RSPSA..97..374R |doi=10.1098/rspa.1920.0040 |issn=0950-1207 |doi-access=free}}</ref>)
 |[[James Chadwick]] (1932) <ref>{{cite journal |date=1932 |title=The existence of a neutron |journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character |language=en |volume=136 |issue=830 |pages=692–708 |doi=10.1098/rspa.1932.0112 |bibcode=1932RSPSA.136..692C |issn=0950-1207|last1=Chadwick |first1=J. |doi-access=free }}</ref>
 |The second [[nucleon]].
 |-
 |[[antiparticle]]s
 |&nbsp;
 |[[Paul Dirac]] (1928)<ref>{{cite journal |date=1928 |title=The quantum theory of the electron |journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character |language=en |volume=117 |issue=778 |pages=610–624 |doi=10.1098/rspa.1928.0023 |bibcode=1928RSPSA.117..610D |issn=0950-1207|last1=Dirac |first1=P. A. M. |doi-access=free }}</ref>
 |[[Carl D. Anderson]] ({{subatomic particle|positron|link=yes}}, 1932)
 |Revised explanation uses [[CPT symmetry]].
 |-
 |[[pion]]s {{subatomic particle|pion}}
 |composite ([[meson]]s)
 |[[Hideki Yukawa]] (1935)
 |[[César Lattes]], [[Giuseppe Occhialini]], [[Cecil Powell]] (1947)
 |Explains the [[nuclear force]] between nucleons. The first meson (by modern definition) to be discovered.
 |-
 |[[muon]] {{subatomic particle|muon}}
 |elementary (lepton)
 |{{no|''never''}}
 |Carl D. Anderson (1936)<ref>{{cite journal |last1=Anderson |first1=Carl D. |last2=Neddermeyer |first2=Seth H. |date=1936-08-15 |title=Cloud Chamber Observations of Cosmic Rays at 4300 Meters Elevation and Near Sea-Level |url=https://link.aps.org/doi/10.1103/PhysRev.50.263 |journal=Physical Review |language=en |volume=50 |issue=4 |pages=263–271 |doi=10.1103/PhysRev.50.263 |bibcode=1936PhRv...50..263A |issn=0031-899X|url-access=subscription }}</ref>
 |Called a "meson" at first; but today classed as a [[lepton]].
 |-
|[[tau (particle)|tau]] {{subatomic particle|tau}}
 |elementary ([[lepton]])
 |[[Antonio Zichichi]] (1960) <ref>
{{cite book
 |last=Zichichi |first=A.
 |title=History of Original Ideas and Basic Discoveries in Particle Physics
 |publisher=Springer
 |year=1996
 |editor-last=Newman |editor-first=H.B.
 |editor-last2=Ypsilantis |editor-first2=T.
 |series=NATO ASI Series (Series B: Physics)
 |volume=352
 |location=Boston, MA
 |pages=227–275
 |chapter=Foundations of sequential heavy lepton searches
 |chapter-url=https://cds.cern.ch/record/268975/files/laa-94-027.pdf}}</ref>
 |[[Martin Lewis Perl]] (1975)
 |-
|[[kaon]]s {{subatomic particle|kaon}}
 |composite (mesons)
 |{{no|''never''}}
 |[[George Rochester|G. D. Rochester]], [[Clifford Charles Butler|C. C. Butler]] (1947)<ref>{{cite journal |last1=Rochester |first1=G. D. |last2=Butler |first2=C. C. |date=December 1947 |title=Evidence for the Existence of New Unstable Elementary Particles |journal=[[Nature (journal)|Nature]] |volume=160 |issue=4077 |pages=855–857 |bibcode=1947Natur.160..855R |doi=10.1038/160855a0 |issn=0028-0836 |pmid=18917296 |s2cid=33881752}}</ref>
 |Discovered in [[cosmic ray]]s. The first [[strange particle]].
 |-
 |[[lambda baryon]]s {{subatomic particle|Lambda}}
 |composite (baryons)
 |{{no|''never''}}
 |[[University of Melbourne]] ({{subatomic particle|Lambda0}}, 1950)<ref>Some sources such as {{cite web |url=http://hyperphysics.phy-astr.gsu.edu/Hbase/Particles/quark.html#c4 |title=The Strange Quark}} indicate 1947.</ref>
 |The first [[hyperon]] discovered.
 |-
 |[[neutrino]] {{math|{{subatomic particle|neutrino}}}}
 |elementary (lepton)
 |[[Wolfgang Pauli]] (1930), named by [[Enrico Fermi]]
 |[[Clyde Cowan]], [[Frederick Reines]] ({{subatomic particle|electron neutrino|link=yes}}, 1956)
 |Solved the problem of energy [[spectrum]] of [[beta decay]].
 |-
 |[[quark]]s<br />({{subatomic particle|up quark}}, {{subatomic particle|down quark}}, {{subatomic particle|strange quark}})
 |elementary
 |[[Murray Gell-Mann]], [[George Zweig]] (1964)
 | colspan=2 {{No}} particular confirmation event for the [[quark model]].
 |-
 |[[charm quark]] {{subatomic particle|charm quark}}
 |elementary (quark)
 |[[Sheldon Glashow]], [[John Iliopoulos]], [[Luciano Maiani]] (1970)
 |[[Burton Richter|B. Richter]], [[Samuel C. C. Ting|S. C. C. Ting]] ({{SubatomicParticle|J/psi|link=yes}}, 1974)
 |
 |-
 |[[bottom quark]] {{subatomic particle|bottom quark}}
 |elementary (quark)
 |[[Makoto Kobayashi (physicist)|Makoto Kobayashi]], [[Toshihide Maskawa]] (1973)
 |[[Leon M. Lederman]] ({{SubatomicParticle|Upsilon|link=yes}}, 1977)
 |
 |-
 |[[gluon]]s
 |elementary (quantum)
 |[[Harald Fritzsch]], [[Murray Gell-Mann]] (1972)<ref>
  {{cite journal
   |last1=Fritzsch |first1=Harald
   |last2=Gell-Mann |first2=Murray
   |title=Current algebra: Quarks and what else?
   |journal=EConf
   |date=1972 |volume=C720906V2 |pages=135–165
   |arxiv=hep-ph/0208010
  }}</ref>
 |[[DESY]] (1979)
 |
 |-
 |[[W and Z bosons|weak gauge bosons]] {{SubatomicParticle|W boson+-}}, {{SubatomicParticle|Z boson0}}
 |elementary (quantum)
 |[[Sheldon Glashow]], [[Steven Weinberg]], [[Abdus Salam]] (1968)<ref>
 {{cite journal
  |last=Glashow |first=Sheldon L.
  |date=1961
  |title=Partial-symmetries of weak interactions
  |url=https://www.sciencedirect.com/science/article/abs/pii/0029558261904692
  |journal=Nuclear Physics
  |language=en
  |volume=22 |issue=4 |pages=579–588
  |doi=10.1016/0029-5582(61)90469-2|bibcode=1961NucPh..22..579G
 |url-access=subscription
  }}</ref><ref>
 {{cite journal
  |last=Weinberg |first=Steven
  |date=1967
  |title=A Model of Leptons
  |journal=Physical Review Letters
  |language=en
  |volume=19 |issue=21 |pages=1264–1266
  |bibcode=1967PhRvL..19.1264W
  |doi=10.1103/PhysRevLett.19.1264 |doi-access=free }}</ref><ref>
 {{cite journal
  |last=Salam |first=Abdus
  |date=1968
  |title=Weak and electromagnetic interactions
  |url=https://inspirehep.net/literature/53083
  |journal=Conf. Proc. C
  |series=World Scientific Series in 20th Century Physics
 |language=en
  |volume=680519 |pages=367–377
  |doi=10.1142/9789812795915_0034|isbn=978-981-02-1662-7
 |url-access=subscription
  }}</ref>
 |[[CERN]] (1983)
 |Properties verified through the 1990s.
 |-
 |[[top quark]] {{subatomic particle|top quark}}
 |elementary (quark)
 |[[Makoto Kobayashi (physicist)|Makoto Kobayashi]], [[Toshihide Maskawa]] (1973)<ref>{{cite journal |last1=Kobayashi |first1=Makoto |last2=Maskawa |first2=Toshihide |date=1973 |title=C P Violation in the Renormalizable Theory of Weak Interaction |url=https://academic.oup.com/ptp/article-lookup/doi/10.1143/PTP.49.652 |journal=Progress of Theoretical Physics |language=en |volume=49 |issue=2 |pages=652–657 |bibcode=1973PThPh..49..652K |doi=10.1143/PTP.49.652 |issn=0033-068X |s2cid=14006603 |hdl-access=free |hdl=2433/66179}}</ref>
 |[[Fermilab]] (1995)<ref>{{cite journal |last1=Abachi |first1=S. |last2=Abbott |first2=B. |last3=Abolins |first3=M. |last4=Acharya |first4=B. S. |last5=Adam |first5=I. |last6=Adams |first6=D. L. |last7=Adams |first7=M. |last8=Ahn |first8=S. |last9=Aihara |first9=H. |last10=Alitti |first10=J. |last11=Álvarez |first11=G. |last12=Alves |first12=G. A. |last13=Amidi |first13=E. |last14=Amos |first14=N. |last15=Anderson |first15=E. W. |date=1995-04-03 |title=Observation of the Top Quark |url=https://link.aps.org/doi/10.1103/PhysRevLett.74.2632 |journal=Physical Review Letters |language=en |volume=74 |issue=14 |pages=2632–2637 |doi=10.1103/PhysRevLett.74.2632 |pmid=10057979 |arxiv=hep-ex/9503003 |bibcode=1995PhRvL..74.2632A |hdl=1969.1/181526 |s2cid=42826202 |issn=0031-9007}}</ref>
 |Does not [[hadronization|hadronize]], but is necessary to complete the Standard Model.
 |-
 |[[Higgs boson]]
 |elementary (quantum)
 |[[Peter Higgs]] (1964)<ref>{{cite web |date=2014-02-12 |title=Letters from the Past – A PRL Retrospective |url=https://journals.aps.org/prl/50years/milestones |access-date=2022-08-22 |website=Physical Review Letters |language=en}}</ref><ref>{{cite journal |last=Higgs |first=Peter W. |date=1964-10-19 |title=Broken Symmetries and the Masses of Gauge Bosons |journal=Physical Review Letters |language=en |volume=13 |issue=16 |pages=508–509 |doi=10.1103/PhysRevLett.13.508 |bibcode=1964PhRvL..13..508H |issn=0031-9007|doi-access=free }}</ref>
 |CERN (2012)<ref>{{cite journal |last1=Aad |first1=G. |last2=Abajyan |first2=T. |last3=Abbott |first3=B. |last4=Abdallah |first4=J. |last5=Abdel Khalek |first5=S. |last6=Abdelalim |first6=A.A. |last7=Abdinov |first7=O. |last8=Aben |first8=R. |last9=Abi |first9=B. |last10=Abolins |first10=M. |last11=AbouZeid |first11=O.S. |last12=Abramowicz |first12=H. |last13=Abreu |first13=H. |last14=Acharya |first14=B.S. |last15=Adamczyk |first15=L. |date=2012 |title=Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC |url=https://linkinghub.elsevier.com/retrieve/pii/S037026931200857X |journal=Physics Letters B |language=en |volume=716 |issue=1 |pages=1–29 |doi=10.1016/j.physletb.2012.08.020|arxiv=1207.7214 |bibcode=2012PhLB..716....1A |s2cid=119169617 }}</ref>
 |Only known spin zero elementary particle.<ref>{{cite journal |last1=Jakobs |first1=Karl |last2=Zanderighi |first2=Giulia |date=2024-02-05 |title=The profile of the Higgs boson: status and prospects |url=https://royalsocietypublishing.org/doi/10.1098/rsta.2023.0087 |journal=Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences |language=en |volume=382 |issue=2266 |doi=10.1098/rsta.2023.0087 |pmid=38104616 |issn=1364-503X|arxiv=2311.10346 |bibcode=2024RSPTA.38230087J }}</ref>
 |-
 |[[tetraquark]]
 |composite
 | {{dunno}}
 |[[Zc(3900)|Z<sub>c</sub>(3900)]], 2013, <small>yet to be confirmed as a tetraquark</small>
 |A new class of hadrons.
 |-
 |[[pentaquark]]
 |composite
 | {{dunno}}
 | colspan=2 |Yet another class of hadrons. {{As of|2019}} several are thought to exist.
 |-
 |[[graviton]]
 |elementary (quantum)
 |Albert Einstein (1916)
 |
 |Interpretation of a [[gravitational wave]] as particles is controversial.<ref>{{cite web |last=Moskowitz |first=Clara |date=March 31, 2014 |title=Multiverse Controversy Heats Up over Gravitational Waves |url=https://www.scientificamerican.com/article/multiverse-controversy-inflation-gravitational-waves/ |access-date=2022-08-22 |website=[[Scientific American]] |language=en}}</ref>
 |-
 |[[magnetic monopole]]
 |elementary (unclassified)
 |Paul Dirac (1931)<ref>{{cite journal |last1=Dirac |first1=Paul A. M. |date=1931 |title=Quantised singularities in the electromagnetic field |url=https://royalsocietypublishing.org/doi/10.1098/rspa.1931.0130 |journal=Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character |language=en |volume=133 |issue=821 |pages=60–72 |bibcode=1931RSPSA.133...60D |doi=10.1098/rspa.1931.0130 |issn=0950-1207|url-access=subscription |doi-access=free }}</ref>
 |{{not yet|''hypothetical''}}<ref name=PDG-2024>{{cite journal |last1=Navas |first1=S. |last2=Amsler |first2=C. |last3=Gutsche |first3=T. |last4=Hanhart |first4=C. |last5=Hernández-Rey |first5=J. J. |last6=Lourenço |first6=C. |last7=Masoni |first7=A. |last8=Mikhasenko |first8=M. |last9=Mitchell |first9=R. E. |last10=Patrignani |first10=C. |last11=Schwanda |first11=C. |last12=Spanier |first12=S. |last13=Venanzoni |first13=G. |last14=Yuan |first14=C. Z. |last15=Agashe |first15=K. |date=2024-08-01 |title=Review of Particle Physics |url=https://link.aps.org/doi/10.1103/PhysRevD.110.030001 |journal=Physical Review D |language=en |volume=110 |issue=3 |page=030001 |doi=10.1103/PhysRevD.110.030001 |issn=2470-0010|hdl=20.500.11850/695340 |hdl-access=free }}</ref>{{rp|loc=25}}
 |
|}

== See also ==
{{portal|Physics}}
{{clear}}
{{div col begin|colwidth=16em}}
* ''[[Atom: Journey Across the Subatomic Cosmos]]'' (book)
* ''[[Atom: An Odyssey from the Big Bang to Life on Earth...and Beyond]]'' (book)
* [[CPT invariance]]
* [[Dark matter]]
* [[Hot spot effect in subatomic physics]]
* [[List of fictional elements, materials, isotopes and atomic particles]]
* [[List of particles]]
* [[Poincaré symmetry]]
{{div col end}}

== References ==
{{Reflist|refs=
<ref name="protonDebate">There was early debate on what to name the proton as seen in the follow commentary articles by [https://www.nature.com/articles/106502b0 Soddy 1920] and [https://www.nature.com/articles/106467a0 Lodge 1920].</ref>
}}

== Further reading ==
=== General readers ===
* {{cite book |author-link=Richard Feynman |url=https://books.google.com/books?id=QKrU9Ir0cSsC |title=Elementary particles and the laws of physics: the 1986 Dirac memorial lectures |author-link2=Steven Weinberg |date=2001 |publisher=[[Cambridge University Press]] |isbn=978-0-521-65862-1 |editor-last=Feynman |editor-first=Richard P. |edition=Repr |location=Cambridge |editor-last2=Weinberg |editor-first2=Steven}}
* {{cite book |last=Greene |first=Brian |author-link=Brian Greene |title=The elegant universe: superstrings, hidden dimensions, and the quest for the ultimate theory |title-link=The Elegant Universe |date=2003 |publisher=Norton |isbn=978-0-393-05858-1 |location=New York; London, England}}
* {{cite book |last=Oerter |first=Robert |title=The theory of almost everything: the Standard Model, the unsung triumph of modern physics |date=2006 |publisher=[[Pi Press]] |isbn=978-0-452-28786-0 |location=New York, New York}}
* {{cite book |last=Schumm |first=Bruce A. |url=https://books.google.com/books?id=htJbAf7xA_oC |title=Deep down things: the breathtaking beauty of particle physics |date=2004 |publisher=[[Johns Hopkins University Press]] |isbn=978-0-8018-7971-5 |location=Baltimore, Maryland}}
* {{cite book |last=Veltman |first=Martinus |author-link=Martinus Veltman |url=https://archive.org/details/factsmysteriesin0000velt |title=Facts and mysteries in elementary particle physics |date=2003 |publisher=[[World Scientific]] |isbn=978-981-238-148-4 |location=River Edge, New Jersey |url-access=registration}}

=== Textbooks ===
* {{cite book |last1=Coughlan |first1=Guy D. |url=https://books.google.com/books?id=R0eNPyk0ENAC |title=The ideas of particle physics: an introduction for scientists |last2=Dodd |first2=J. E. |last3=Gripaios |first3=Ben M. |date=2006 |publisher=[[Cambridge University Press]] |isbn=978-0-521-67775-2 |edition=3rd |location=Cambridge}} An undergraduate text for those not majoring in physics.
* {{cite book |last=Griffiths |first=David J. |author-link=David J. Griffiths |url=https://books.google.com/books?id=Wb9DYrjcoKAC |title=Introduction to elementary particles |date=2007 |publisher=[[Wiley (publisher)|Wiley]] |isbn=978-0-471-60386-3 |location=Weinheim}}
* {{cite book |last=Kane |first=Gordon L. |author-link=Gordon L. Kane |url=https://books.google.com/books?id=54PuDQAAQBAJ |title=Modern elementary particle physics |date=2017 |publisher=[[Cambridge University Press]] |isbn=978-1-107-16508-3 |edition=2nd |location=Cambridge, England, United Kingdom; New York, New York, USA}}

== External links ==
{{Commons category|Subatomic particles}}
* [http://pdg.lbl.gov/ University of California: Particle Data Group.]

{{Particles}}

[[Category:Subatomic particles]]
[[Category:Quantum mechanics]]