Editing Elementary charge (section)

=== Tests  of the universality of elementary charge ===
{| class="wikitable"
|+ 
|-
! Particle !! Expected charge !! Experimental constraint !! Notes
|-
| electron || <math>q_{\text{e}^-}=-e</math> || exact || by definition
|-
| proton || <math>q_\text{p}=e</math> || <math>\left|{q_\text{p} - e}\right| < 10^{-21}e</math> || by finding no measurable sound when an alternating electric field is applied to [[sulfur hexafluoride|SF<sub>6</sub>]] gas in a spherical resonator<ref>
{{cite journal
 | last1      = Bressi | first1     = G.
 | last2      = Carugno | first2     = G.
 | last3      = Della Valle | first3     = F.
 | last4      = Galeazzi | first4     = G.
 | last5      = Sartori | first5      = G.
 | date       = 2011
 | title      = Testing the neutrality of matter by acoustic means in a spherical resonator
 | journal    = Physical Review A
 | volume     = 83
 | number     = 5
 | pages      = 052101
 | doi        = 10.1103/PhysRevA.83.052101
 | arxiv = 1102.2766
 | s2cid = 118579475
}}</ref>
|-
| [[positron]] || <math>q_{\text{e}^+}=e</math> || <math>\left|{q_{\text{e}^+} - e}\right| < 10^{-9}e</math> || by combining the best measured value of the antiproton charge (below) with the low limit placed on antihydrogen's net charge by the [[ALPHA Collaboration]] at [[CERN]].<ref>
{{cite journal
 | display-authors = etal
 | last1 = Ahmadi | first1 = M.
 | date       = 2016
 | title      = An improved limit on the charge of antihydrogen from stochastic acceleration
 | url        = https://www.nature.com/articles/nature16491.pdf
 | journal    = Nature
 | volume     = 529
 | issue      = 7586
 | pages      = 373–376
 | doi        = 10.1038/nature16491
 | pmid = 26791725
 | s2cid = 205247209
 | access-date = May 1, 2022
}}</ref>
|-
| [[antiproton]] || <math>q_{\bar{\text{p}}}=-e</math> || <math>\left|{q_{\bar{\text{p}}} + q_\text{p}}\right| < 10^{-9}e</math> || Hori et al.<ref>
{{cite journal
 | display-authors = etal
 | last1 = Hori | first = M.
 | date       = 2011
 | title      = Two-photon laser spectroscopy of antiprotonic helium and the antiproton-to-electron mass ratio.
 | journal    = Nature
 | volume     = 475
 | issue = 7357
 | pages      = 484–488
 | doi        = 10.1038/nature10260
 | pmid = 21796208
 | arxiv = 1304.4330
 | s2cid = 4376768
}}</ref> as cited in antiproton/proton charge difference listing of the [[Particle Data Group]]<ref>
{{cite journal
 | display-authors = etal
 | last1 = Olive | first1 = K. A.
 | date       = 2014
 | title      = Review of particle physics
 | journal    = Chinese Physics C
 | volume     = 38
 | number     = 9
 | pages      = 090001
 | doi        = 10.1088/1674-1137/38/9/090001
 | s2cid = 118395784
 | url = http://bib-pubdb1.desy.de/record/172097/files/PUBDB-2014-03548.pdf
}}</ref> The Particle Data Group article has a link to the current online version of the particle data.
|}