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{{Short description|Class of subatomic particle}}
{{Other uses}}
{{Use dmy dates|date=October 2020}}
[[File:Bosons-Hadrons-Fermions-RGB-png2.png|thumb|upright=1.6|Bosons form one of the two fundamental classes of [[subatomic particle]], the other being [[fermion]]s. All subatomic particles must be one or the other. A composite particle ([[hadron]]) may fall into either class depending on its composition.]]

In [[particle physics]], a '''boson''' ({{IPAc-en|ˈ|b|oʊ|z|ɒ|n}}<ref>{{Cite encyclopedia |url=http://www.lexico.com/definition/boson |archive-url=https://web.archive.org/web/20210709191352/https://www.lexico.com/definition/boson |url-status=dead |archive-date=9 July 2021 |title=boson |dictionary=[[Lexico]] UK English Dictionary |publisher=[[Oxford University Press]]}}</ref> {{IPAc-en|ˈ|b|oʊ|s|ɒ|n}}<ref>{{cite book|last=Wells|first=John C.|title=Longman pronunciation dictionary|publisher=Longman|year=1990|isbn=978-0582053830|location=Harlow, England}} entry "Boson"</ref>) is a [[subatomic particle]] whose [[spin quantum number]] has an [[integer]] value (0, 1, 2, ...). Bosons form one of the two fundamental classes of subatomic particle, the other being [[fermion]]s, which have odd half-integer spin ({{frac|1|2}}, {{frac|3|2}}, {{frac|5|2}}, ...). Every observed subatomic particle is either a boson or a fermion. [[Paul Dirac]] coined the name ''boson'' to commemorate the contribution of [[Satyendra Nath Bose]], an Indian physicist.

Some bosons are [[elementary particle]]s occupying a special role in particle physics, distinct from the role of fermions (which are sometimes described as the constituents of "ordinary matter"). Certain elementary bosons (e.g. [[gluon]]s) act as [[force carrier]]s, which give rise to forces between other particles, while one (the [[Higgs boson]]) contributes to the phenomenon of [[mass]]. Other bosons, such as [[meson]]s, are composite particles made up of smaller constituents.
	
Outside the realm of particle physics, multiple identical composite bosons (in this context sometimes known as '<nowiki/>'''bose particles'''<nowiki/>') behave at high densities or low temperatures in a characteristic manner described by [[Bose–Einstein statistics]]: for example a gas of [[helium-4]] atoms becomes a [[Superfluid helium-4|superfluid]] at temperatures close to absolute zero. Similarly, [[superconductivity]] arises because some [[quasiparticle]]s, such as [[Cooper pair]]s, behave in the same way.

== Name ==
The name ''boson'' was coined by [[Paul Dirac]]<ref>{{cite book|title=Notes on Dirac's lecture ''Developments in Atomic Theory'' at Le Palais de la Découverte, 6&nbsp;December 1945|publisher=UKNATARCHI Dirac Papers|id=BW83/2/257889}}</ref><ref>{{Cite book|last=Farmelo|first=Graham|url=https://books.google.com/books?id=qsodmIGD0fMC&q=farmelo+graham+the+strangest+man|title=The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom|date=2009-08-25|publisher=Basic Books|isbn=9780465019922|pages=331|language=en}}</ref> to commemorate the contribution of [[Satyendra Nath Bose]], an [[Indian people|Indian]] physicist. When Bose was a reader (later professor) at the [[University of Dhaka]], [[Bengal]] (now in [[Bangladesh]]),<ref name="AP-20120710">{{cite news|last=Daigle|first=Katy|date=10 July 2012|title=India: Enough about Higgs, let's discuss the boson|agency=[[Associated Press]]|url=http://apnews.excite.com/article/20120710/D9VU1DRG0.html|access-date=10 July 2012}}</ref><ref name="NYT-20120919">{{cite news|last=Bal|first=Hartosh Singh|date=19 September 2012|title=The Bose in the Boson|work=[[The New York Times]]|department=Latitude (blog)|url=http://latitude.blogs.nytimes.com/2012/09/19/indians-clamor-for-credit-for-the-bose-in-boson/|url-status=dead|access-date=21 September 2012|archive-url=https://web.archive.org/web/20120922024310/http://latitude.blogs.nytimes.com/2012/09/19/indians-clamor-for-credit-for-the-bose-in-boson/|archive-date=22 September 2012}}</ref> he and [[Albert Einstein]] developed the theory characterising such particles, now known as [[Bose–Einstein statistics]] and [[Bose–Einstein condensate]].<ref>{{cite news|date=4 July 2012|title=Higgs boson: The poetry of subatomic particles|work=BBC News|url=https://www.bbc.co.uk/news/magazine-18708741|access-date=6 July 2012}}</ref>

== Elementary bosons ==
{{Standard model of particle physics|cTopic=[[Elementary particle]]s}}
{{See also|List of particles#Bosons}}

All observed [[elementary particles]] are either bosons (with integer spin) or [[fermions]] (with odd half-integer spin).<ref name="DarkMatter">{{cite book|author=Carroll, Sean|title=Guidebook|publisher=The Teaching Company|year=2007|isbn=978-1598033502|series=Dark Matter, Dark Energy: The dark side of the universe|at=Part&nbsp;2, p.&nbsp;43|quote=...&nbsp;boson: A force-carrying particle, as opposed to a matter particle (fermion). Bosons can be piled on top of each other without limit. Examples are photons, gluons, gravitons, weak bosons, and the Higgs boson. The spin of a boson is always an integer: 0, 1, 2, and so on&nbsp;...}}</ref> Whereas the elementary particles that make up ordinary matter ([[lepton]]s and [[quark]]s) are fermions, elementary bosons occupy a special role in particle physics. They act either as [[force carrier]]s which give rise to forces between other particles, or in one case give rise to the phenomenon of [[mass]].

According to the [[Standard Model of Particle Physics]] there are five elementary bosons:
* One ''[[scalar boson]]'' (spin = 0)  
**{{Subatomic particle|link=yes|Higgs Boson}}  [[Higgs boson]] – the particle that contributes to the phenomenon of [[mass]] via the [[Higgs mechanism]]
* Four ''[[vector boson]]s'' (spin = 1) that act as [[force carriers]]. These are the [[gauge boson]]s:
** {{Subatomic particle|link=yes|Photon}}  [[Photon]] – the force carrier of the [[electromagnetic field]]
** {{Subatomic particle|link=yes|Gluon}}  [[Gluon]]s (eight different types) – force carriers that mediate the [[Strong interaction|strong force]]
** {{Subatomic particle|link=yes|Z boson}}  [[W and Z bosons|Neutral weak boson]] – the force carrier that mediates the [[weak interaction|weak force]]
** {{Subatomic particle|link=yes|W boson+-}}&nbsp; [[W and Z bosons|Charged weak boson]]s (two types) – also force carriers that mediate the weak force

* <span class="anchor" id="tensor_boson_anchor"></span> A ''second order tensor boson'' (spin = 2) called the [[graviton]] (G) has been hypothesised as the force carrier for [[Gravitational force|gravity]], but so far all attempts to incorporate gravity into the Standard Model have failed.{{efn|
Despite being the carrier of the gravitational force which interacts with mass, most attempts at [[quantum gravity]] have expected the graviton to have no mass, just like the photon has no electric charge, and the [[W and Z bosons]] have no [[flavour (particle physics)|"flavour"]].
}}

== Composite bosons ==
{{see also|List of particles#Composite particles}}

Composite particles (such as [[hadron]]s, [[atomic nucleus|nuclei]], and [[atom]]s) can be bosons or fermions depending on their constituents. Since bosons have integer [[Spin (physics)|spin]] and fermions odd half-integer spin, any composite particle made up of an even number of fermions is a boson.

Composite bosons include:
* All [[meson]]s of every type
* Stable nuclei with even [[mass number]]s such as [[deuterium]], [[helium-4]] (the [[alpha particle]]),<ref>
{{cite journal
 |last1=Qaim     |first1=Syed M.         |last2=Spahn    |first2=Ingo
 |last3=Scholten |first3=Bernhard        |last4=Neumaier |first4=Bernd
 |date=June 8, 2016
 |title=Uses of alpha particles, especially in nuclear reaction studies and medical radionuclide production
 |journal=Radiochimica Acta
 |volume=104 |issue=9 |page=601
 |doi=10.1515/ract-2015-2566  |s2cid=56100709
 |url=https://www.degruyter.com/document/doi/10.1515/ract-2015-2566/html
 |access-date=May 22, 2021
}}
</ref> [[carbon-12]], [[lead-208]], and many others.<ref group="lower-alpha">
[[Even and odd atomic nuclei|Even-mass-number nuclides]] comprise {{sfrac|&nbsp;153&nbsp;| 254 }} = 60% of all stable nuclides. They are bosons, i.e. they have integer spin, and almost all of them (148 of the 153) are even-proton / even-neutron (EE) nuclides. The EE nuclides necessarily have spin&nbsp;0 because of pairing. The remaining 5&nbsp;stable bosonic nuclides are odd-proton / odd-neutron (OO) stable nuclides (see ''{{section link|Even and odd atomic nuclei#Odd proton, odd neutron}}''). The five odd–odd bosonic nuclides are:
{{div col begin|colwidth=3em}}
: {{nuclide|Hydrogen|2|link=yes}}
: {{nuclide|Lithium|6|link=yes}}
: {{nuclide|Boron|10|link=yes}}
: {{nuclide|Nitrogen|14|link=yes}}
: [[Tantalum-180m|{{nuclide|Tantalum|180|m}}]]
{{div col end}}
Each of the five has integer, nonzero spin.
</ref>

As [[Quantum mechanics|quantum particles]], the behaviour of multiple indistinguishable bosons at high densities is described by Bose–Einstein statistics. One characteristic which becomes important in [[superfluidity]] and other applications of Bose–Einstein condensates is that there is no restriction on the number of bosons that may occupy the same [[quantum state]]. As a consequence, when for example a gas of [[helium-4]] atoms is cooled to temperatures very close to [[absolute zero]] and the [[kinetic energy]] of the particles becomes negligible, it condenses into a low-energy state and becomes a [[Superfluid helium-4|superfluid]].

== Quasiparticles ==
Certain [[quasiparticle]]s are observed to behave as bosons and to follow [[Bose–Einstein statistics]], including Cooper pairs, [[plasmon]]s and [[phonon]]s.<ref name="Jr.2004">{{cite book|author1-link=|author=Poole, Charles P. Jr.|url=https://books.google.com/books?id=CXwrqM2hU0EC|title=Encyclopedic Dictionary of Condensed Matter Physics|date=11 March 2004|publisher=Academic Press|isbn=978-0-08-054523-3}}</ref>{{rp|130}}

== See also ==
* {{annotated link|Anyon}}
* {{annotated link|Bose gas}}
* {{annotated link|Parastatistics}}

== Explanatory notes ==
{{notelist}}

== References ==
{{reflist}}

{{particles}}

{{Authority control}}

[[Category:Quantum field theory]]
[[Category:Atomic physics]]
[[Category:Bosons| ]]
[[Category:Condensed matter physics]]