Editing Elementary particle (section)

=== 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>