Editing Elementary particle (section)

==== 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.