Editing Elementary particle (section)

== Standard Model ==
{{Main|Standard Model}}
The Standard Model of particle physics contains 12 flavors of elementary [[fermion]]s, plus their corresponding [[antiparticle]]s, as well as elementary bosons that mediate the forces and the [[Higgs boson]], which was reported on July 4, 2012, as having been likely detected by the two main experiments at the [[Large Hadron Collider]] ([[ATLAS experiment|ATLAS]] and [[Compact Muon Solenoid|CMS]]).<ref name=PFI /> The Standard Model is widely considered to be a provisional theory rather than a truly fundamental one, however, since it is not known if it is compatible with [[Albert Einstein|Einstein]]'s [[general relativity]]. There may be hypothetical elementary particles not described by the Standard Model, such as the [[graviton]], the particle that would carry the [[gravity|gravitational force]], and [[superpartner|sparticles]], [[supersymmetry|supersymmetric]] partners of the ordinary particles.<ref>{{cite journal |last=Holstein |first=Barry R. |date=November 2006 |title=Graviton physics |journal=[[American Journal of Physics]] |volume=74 |issue=11 |pages=1002–1011 |doi=10.1119/1.2338547 |arxiv=gr-qc/0607045 |bibcode=2006AmJPh..74.1002H |s2cid=15972735 }}</ref>

=== Fundamental fermions ===
{{Main|Fermion}}

The 12&nbsp;fundamental fermions are divided into 3&nbsp;[[generation (particle physics)|generations]] of 4&nbsp;particles each. Half of the fermions are [[lepton]]s, three of which have an electric charge of −1&nbsp;''e'', called the electron ({{Subatomic particle|electron-}}), the [[muon]] ({{Subatomic particle|muon-}}), and the [[tau (particle)|tau]] ({{Subatomic particle|tau-}}); the other three leptons are [[neutrino]]s ({{Subatomic particle|electron neutrino}}, {{Subatomic particle|muon neutrino}}, {{Subatomic particle|tau neutrino}}), which are the only elementary fermions with neither electric nor [[color charge]]. The remaining six particles are [[quark]]s (discussed below).

==== Generations ====
{| class="wikitable"  style="text-align:center;"
|+ Particle generations
|-
!colspan="6"| [[Lepton]]s
|-
|colspan="2"| ''First generation''
|colspan="2"| ''Second generation''
|colspan="2"| ''Third generation''
|-
|''Name'' || ''Symbol'' || ''Name'' || ''Symbol'' || ''Name'' || ''Symbol''
|-
| [[electron]] || {{Subatomic particle|electron-}} || [[muon]] || {{math|{{Subatomic particle|muon-}}}} || [[tau (particle)|tau]] || {{math|{{Subatomic particle|tau-}}}}
|-
| [[electron neutrino]] || {{math|{{Subatomic particle|electron neutrino}}}} || [[muon neutrino]]|| {{math|{{Subatomic particle|Muon neutrino}}}} || [[tau neutrino]] || {{math|{{Subatomic particle|Tau neutrino}}}}
|-
!colspan="6"| [[Quark]]s
|-
|colspan="2"| ''First generation''
|colspan="2"| ''Second generation''
|colspan="2"| ''Third generation''
|-
| [[up quark]] || {{Subatomic particle|Up quark}} || [[charm quark]] || c || [[top quark]] || {{Subatomic particle|Top quark}}
|-
| [[down quark]] || {{Subatomic particle|Down quark}} || [[strange quark]] || {{Subatomic particle|Strange quark}} || [[bottom quark]]|| {{Subatomic particle|Bottom quark}}
|}

==== Mass ====
The following table lists current measured masses and mass estimates for all the fermions, using the same scale of measure: [[Electronvolt|millions of electron-volts]] relative to square of light speed (MeV/''c''<sup>2</sup>). For example, the most accurately known quark mass is of the top quark ({{Subatomic particle|top quark}}) at {{val|172.7|ul=GeV/c2}}, estimated using the [[on-shell scheme]].

{| class="wikitable" style="margin:0 0 1em 1em;"
|+ Current values for elementary fermion masses
|-
! Particle symbol
! Particle name
! Mass value
! Quark mass estimation scheme (point)
|-
| {{math|{{Subatomic particle|electron neutrino}}}}, {{math|{{Subatomic particle|muon neutrino}}}}, {{math|{{Subatomic particle|tauon neutrino}}}}
| [[Neutrino]]<br />(any&nbsp;type)
| style="text-align:right;" | < {{val|2|ul=eV/c2}}<ref>{{cite journal |last1=Tanabashi |first1=M. |last2=Hagiwara |first2=K. |last3=Hikasa |first3=K. |last4=Nakamura |first4=K. |last5=Sumino |first5=Y. |last6=Takahashi |first6=F. |last7=Tanaka |first7=J. |last8=Agashe |first8=K. |last9=Aielli |first9=G. |last10=Amsler |first10=C. |display-authors=6 |collaboration=Particle Data Group |title=Review of Particle Physics |journal=[[Physical Review D]] |volume=98 |issue=3 |date=2018-08-17 |page=030001 |df=dmy-all |doi=10.1103/physrevd.98.030001 |bibcode=2018PhRvD..98c0001T |pmid=10020536 |doi-access=free|hdl=10044/1/68623 |hdl-access=free }}</ref>
|
|-
| {{Subatomic particle|electron}}
| [[electron]]
| style="text-align:right;" | {{val|0.511|ul=MeV/c2}}
|
|-
| {{Subatomic particle|up quark}}
| [[up quark]]
| style="text-align:right;" | {{val|1.9|ul=MeV/c2}}
| [[MSbar scheme]] ({{mvar|μ}}<sub>{{overline|MS}}</sub> = {{val|2|u=GeV}})
|-
| {{Subatomic particle|down quark}}
| [[down quark]]
| style="text-align:right;" | {{val|4.4|ul=MeV/c2}}
| [[MSbar scheme]] ({{mvar|μ}}<sub>{{overline|MS}}</sub> = {{val|2|u=GeV}})
|-
| {{Subatomic particle|strange quark}}
| [[strange quark]]
| style="text-align:right;" | {{val|87|u=MeV/c2}}
| [[MSbar scheme]] ({{mvar|μ}}<sub>{{overline|MS}}</sub> = {{val|2|u=GeV}})
|-
| {{math|{{Subatomic particle|muon}}}}
| [[muon]]<br />([[mu lepton]])
| style="text-align:right;" | {{val|105.7|ul=MeV/c2}}
|
|-
| {{Subatomic particle|charm quark}}
| [[charm quark]]
| style="text-align:right;" | {{val|1320|ul=MeV/c2}}
| [[MSbar scheme]] ({{mvar|μ}}<sub>{{overline|MS}}</sub> = {{mvar|m}}<sub>c</sub>)
|-
| {{math|{{Subatomic particle|tau}}}}
| [[tauon]] ([[tau&nbsp;lepton]])
| style="text-align:right;" | {{val|1780|ul=MeV/c2}}
|
|-
| {{Subatomic particle|bottom quark}}
| [[bottom quark]]
| style="text-align:right;" | {{val|4240|ul=MeV/c2}}
| [[MSbar scheme]] ({{mvar|μ}}<sub>{{overline|MS}}</sub> = {{mvar|m}}<sub>b</sub>)
|-
| {{Subatomic particle|top quark}}
| [[top quark]]
| style="text-align:right;" | {{val|172700|ul=MeV/c2}}
| [[On-shell scheme]]
|}

Estimates of the values of quark masses depend on the version of [[quantum chromodynamics]] used to describe quark interactions. Quarks are always confined in an envelope of [[gluon]]s that confer vastly greater mass to the [[meson]]s and [[baryon]]s where quarks occur, so values for quark masses cannot be measured directly. Since their masses are so small compared to the effective mass of the surrounding gluons, slight differences in the calculation make large differences in the masses.

==== Antiparticles ====
{{Main|Antimatter}}

There are also 12&nbsp;fundamental fermionic antiparticles that correspond to these 12&nbsp;particles. For example, the [[antielectron]] (positron) {{Subatomic particle|antielectron}} is the electron's antiparticle and has an electric charge of +1&nbsp;''e''.

{| class="wikitable"  style="text-align:center;"
|+ Particle generations
|-
!colspan="6"| [[Lepton|Antileptons]]
|-
|colspan="2"| ''First generation''
|colspan="2"| ''Second generation''
|colspan="2"| ''Third generation''
|-
|''Name'' || ''Symbol'' || ''Name'' || ''Symbol'' || ''Name'' || ''Symbol''
|-
| [[positron]] || {{Subatomic particle|antielectron}} || [[antimuon]] || {{math|{{Subatomic particle|antimuon}}}} || [[antitau]] || {{math|{{Subatomic particle|antitau}}}}
|-
| [[electron antineutrino]] || {{math|{{Subatomic particle|electron antineutrino}}}} || [[muon antineutrino]]|| {{math|{{Subatomic particle|Muon antineutrino}}}} || [[tau antineutrino]] || {{math|{{Subatomic particle|Tau antineutrino}}}}
|-
!colspan="6"| [[Quark|Antiquarks]]
|-
|colspan="2"| ''First generation''
|colspan="2"| ''Second generation''
|colspan="2"| ''Third generation''
|-
| [[up antiquark]] || {{Subatomic particle|Up antiquark}} || [[charm antiquark]] || {{Subatomic particle|Charm antiquark}} || [[top antiquark]] || {{Subatomic particle|Top antiquark}}
|-
| [[down antiquark]] || {{Subatomic particle|Down antiquark}} || [[strange antiquark]] || {{Subatomic particle|Strange antiquark}}  ||  [[bottom antiquark]]|| {{Subatomic particle|Bottom antiquark}}
|}

==== Quarks ====
{{Main|Quark}}
Isolated quarks and antiquarks have never been detected, a fact explained by [[Colour confinement|confinement]]. Every quark carries one of three [[color charge]]s of the [[strong interaction]]; antiquarks similarly carry anticolor. Color-charged particles interact via [[gluon]] exchange in the same way that charged particles interact via [[photon]] exchange. Gluons are themselves color-charged, however, resulting in an amplification of the strong force as color-charged particles are separated. Unlike the [[electromagnetism|electromagnetic force]], which diminishes as charged particles separate, color-charged particles feel increasing force.

Nonetheless, color-charged particles may combine to form color neutral [[composite particle]]s called [[hadron]]s. A quark may pair up with an antiquark: the quark has a color and the antiquark has the corresponding anticolor. The color and anticolor cancel out, forming a color neutral [[meson]]. Alternatively, three quarks can exist together, one quark being "red", another "blue", another "green". These three colored quarks together form a color-neutral [[baryon]]. Symmetrically, three antiquarks with the colors "antired", "antiblue" and "antigreen" can form a color-neutral [[antibaryon]].

Quarks also carry fractional [[electric charge]]s, but, since they are confined within hadrons whose charges are all integral, fractional charges have never been isolated. Note that quarks have electric charges of either {{small|{{sfrac|+|2|3}}}}&nbsp;''e'' or {{small|{{sfrac|−|1|3}}}}&nbsp;''e'', whereas antiquarks have corresponding electric charges of either {{small|{{sfrac|−|2|3}}}}&nbsp;''e'' or&nbsp;{{small|{{sfrac|+|1|3}}}}&nbsp;''e''.

Evidence for the existence of quarks comes from [[deep inelastic scattering]]: firing [[electron]]s at [[atomic nucleus|nuclei]] to determine the distribution of charge within [[nucleon]]s (which are baryons). If the charge is uniform, the [[electric field]] around the proton should be uniform and the electron should scatter elastically. Low-energy electrons do scatter in this way, but, above a particular energy, the protons deflect some electrons through large angles. The recoiling electron has much less energy and a [[jet (particle physics)|jet of particles]] is emitted. This inelastic scattering suggests that the charge in the proton is not uniform but split among smaller charged particles: quarks.

=== Fundamental bosons ===
{{Main|Boson}}

In the Standard Model, vector ([[Spin (physics)|spin]]-1) bosons ([[gluon]]s, [[photon]]s, and the [[W and Z bosons]]) mediate forces, whereas the [[Higgs boson]] (spin-0) is responsible for the intrinsic [[mass]] of particles. Bosons differ from fermions in the fact that multiple bosons can occupy the same quantum state ([[Pauli exclusion principle]]). Also, bosons can be either elementary, like photons, or a combination, like [[meson]]s. The spin of bosons are integers instead of half integers.

==== Gluons ====
{{Main|Gluon}}

Gluons mediate the [[strong interaction]], which join quarks and thereby form [[hadron]]s, which are either [[baryon]]s (three quarks) or [[meson]]s (one quark and one antiquark). Protons and neutrons are baryons, joined by gluons to form the [[atomic nucleus]]. Like quarks, gluons exhibit [[color charge|color]] and anticolor – unrelated to the concept of visual color and rather the particles' strong interactions – sometimes in combinations, altogether eight variations of gluons.

==== Electroweak bosons ====
{{Main|W and Z bosons|Photon}}

There are three [[weak gauge boson]]s: W<sup>+</sup>, W<sup>−</sup>, and Z<sup>0</sup>; these mediate the [[weak interaction]]. The W&nbsp;bosons are known for their mediation in nuclear decay: The W<sup>−</sup> converts a neutron into a proton then decays into an electron and electron-antineutrino pair.
The Z<sup>0</sup> does not convert particle flavor or charges, but rather changes momentum; it is the only mechanism for elastically scattering neutrinos. The weak gauge bosons were discovered due to momentum change in electrons from neutrino-Z exchange. The massless [[photon]] mediates the [[electromagnetism|electromagnetic interaction]]. These four gauge bosons form the electroweak interaction among elementary particles.

==== Higgs boson ====
{{Main|Higgs boson}}

Although the weak and electromagnetic forces appear quite different to us at everyday energies, the two forces are theorized to unify as a single [[electroweak force]] at high energies. This prediction was clearly confirmed by measurements of cross-sections for high-energy electron-proton scattering at the [[Hadron Elektron Ring Anlage|HERA]] collider at [[DESY]]. The differences at low energies is a consequence of the high masses of the W and Z bosons, which in turn are a consequence of the [[Higgs mechanism]]. Through the process of [[spontaneous symmetry breaking]], the Higgs selects a special direction in electroweak space that causes three electroweak particles to become very heavy (the weak bosons) and one to remain with an undefined rest mass as it is always in motion (the photon). On 4 July 2012, after many years of experimentally searching for evidence of its existence, the [[Higgs boson]] was announced to have been observed at CERN's Large Hadron Collider. [[Peter Higgs]] who first posited the existence of the Higgs boson was present at the announcement.<ref>
{{cite news
 |first=Lizzy |last=Davies
 |date=4 July 2014
 |title=Higgs boson announcement live: CERN scientists discover subatomic particle
 |url=https://www.theguardian.com/science/blog/2012/jul/04/higgs-boson-discovered-live-coverage-cern
 |newspaper=[[The Guardian]]
 |access-date=2012-07-06 |df=dmy-all
}}</ref> The Higgs boson is believed to have a mass of approximately {{val|125|u=GeV/c2}}.<ref>
{{cite web
 |first=Lucas |last=Taylor
 |date=4 Jul 2014
 |title=Observation of a new particle with a mass of 125 GeV
 |url=http://cms.web.cern.ch/news/observation-new-particle-mass-125-gev
 |publisher=[[Compact Muon Solenoid|CMS]]
 |access-date=2012-07-06 |df=dmy-all
}}</ref> The [[statistical significance]] of this discovery was reported as 5&nbsp;sigma, which implies a certainty of roughly 99.99994%. In particle physics, this is the level of significance required to officially label experimental observations as a [[Discovery (observation)|discovery]]. Research into the properties of the newly discovered particle continues.

==== Graviton ====

{{Main|Graviton}}

The [[graviton]] is a hypothetical elementary spin-2 particle proposed to mediate gravitation. While it remains undiscovered due to [[Graviton#Experimental observation|the difficulty inherent in its detection]], it is sometimes included in tables of elementary particles.<ref name=PFI /> The conventional graviton is massless, although some models containing massive [[Kaluza–Klein theory|Kaluza–Klein]] gravitons exist.<ref>{{cite journal |arxiv=0910.1535 |bibcode=2010PhLB..682..446C |title=Massless versus Kaluza-Klein gravitons at the LHC |journal=Physics Letters B |volume=682 |issue=4–5 |pages=446–449 |last1=Calmet |first1=Xavier |last2=de Aquino |first2=Priscila |last3=Rizzo |first3=Thomas G. |year=2010 |doi=10.1016/j.physletb.2009.11.045 |hdl=2078/31706|s2cid=16310404 }}</ref>