Editing Subatomic particle (section)

==== Hadrons ====
The word hadron comes from Greek and was introduced in 1962 by [[Lev Okun]].<ref>{{cite conference |first=Lev |last=Okun |author-link=Lev Okun |year=1962 |title=The theory of weak interaction |conference=International Conference on High-Energy Physics |place=CERN, Geneva, CH |book-title=Proceedings of 1962 International Conference on High-Energy Physics at CERN |page=845 |type=plenary talk |bibcode=1962hep..conf..845O}}</ref> Nearly all composite particles contain multiple quarks (and/or antiquarks) bound together by gluons (with a few exceptions with no quarks, such as [[positronium]] and [[muonium]]). Those containing few (≤&nbsp;5) quarks (including antiquarks) are called [[hadron]]s. Due to a property known as [[color confinement]], quarks are never found singly but always occur in hadrons containing multiple quarks. The hadrons are divided by number of quarks (including antiquarks) into the [[baryons]] containing an odd number of quarks (almost always 3), of which the [[proton]] and [[neutron]] (the two [[nucleons]]) are by far the best known; and the [[meson]]s containing an even number of quarks (almost always 2, one quark and one antiquark), of which the [[pion]]s and [[kaon]]s are the best known.

Except for the proton and neutron, all other hadrons are unstable and decay into other particles in microseconds or less. A proton is made of two [[up quark]]s and one [[down quark]], while the neutron is made of two down quarks and one up quark. These commonly bind together into an atomic nucleus, e.g. a helium-4 nucleus is composed of two protons and two neutrons. Most hadrons do not live long enough to bind into nucleus-like composites; those that do (other than the proton and neutron) form [[exotic nuclei]].