Editing Charm quark (section)

=== Theoretical prediction ===
{{See also|GIM mechanism|Scientific wager}}
[[File:K0 decay to muons.svg|thumb|The [[GIM mechanism]] explains the rarity of the decay of a {{SubatomicParticle|antiKaon0|link=true}} into two [[muon]]s by involving the charm quark (c) in the process.]]

In 1964, [[James Bjorken]] and Sheldon Glashow theorized "charm" as a new quantum number.{{sfn|Bjorken|Glashow|1964|p=255}} At the time, there were four known [[lepton]]s—the [[electron]], the [[muon]], and each of their [[neutrino]]s—but Gell-Mann initially proposed only three quarks.{{sfn|Riordan|1987|p=[https://archive.org/details/huntingofquarktr00mich/page/210 210]}} Bjorken and Glashow thus hoped to establish parallels between the leptons and the quarks with their theory.{{sfn|Griffiths|2008|pp=44-45}} According to Glashow, the conjecture came from "aesthetic arguments".{{sfn|Glashow|1976}}

In 1970, Glashow, [[John Iliopoulos]], and [[Luciano Maiani]] proposed a new quark that differed from the three then-known quarks by the [[Charm (quantum number)|charm quantum number]].{{sfn|Glashow|Iliopoulos|Maiani|1970|p=1287}}{{sfn|Appelquist|Barnett|Lane|1978|p=390}} They further predicted the existence of "charmed particles" and offered suggestions on how to experimentally produce them.{{sfn|Glashow|Iliopoulos|Maiani|1970|p=1290–1291}} They also suggested the charmed quark could provide a mechanism—the [[GIM mechanism]]—to facilitate the unification of the [[weak interaction|weak]] and [[electromagnetism|electromagnetic]] forces.{{sfn|Close|1976|p=537}}

At the Conference on Experimental Meson Spectroscopy (EMS) in April 1974, Glashow delivered his paper titled "Charm: An Invention Awaits Discovery". Glashow asserted because [[neutral current]]s were likely to exist, a fourth quark was "sorely needed" to explain the rarity of the decays of certain [[kaon]]s.{{sfn|Riordan|1987|p=[https://archive.org/details/huntingofquarktr00mich/page/297 297]}} He also made several predictions on the properties of charm quarks.{{sfn|Rosner|1998|p=14}} He wagered that, by the next EMS conference in 1976:
{{blockquote|text=
There are just three possibilities:
# Charm is not found, and I eat my hat.
# Charm is found by hadron spectroscopers, and we celebrate.
# Charm is found by outlanders,{{efn|According to Riordan, the word "outlanders" means "other kinds of physicists who did neutrino scattering or measured electron–positron collisions in storage rings."{{sfn|Riordan|1987|p=[https://archive.org/details/huntingofquarktr00mich/page/295 295]}} }} and you eat your hats.{{sfn|Rosner|1998|p=14}}
}}

In July 1974, at the 17th [[International Conference on High Energy Physics]] (ICHEP), Iliopoulos said:
{{blockquote|text=I have won already several bottles of wine by betting for the neutral currents and I am ready to bet now a whole case that if the weak interaction sessions of this Conference were dominated by the discovery of the neutral currents, the entire next Conference will be dominated by the discovery of the charmed particles.{{sfn|Iliopoulos|1974|p=100}}}}

Applying an argument of naturalness to the kaon mass splitting between the K{{su|p=0|b=L}} and K{{su|p=0|b=S}} states, the mass of the charm quark was estimated by [[Mary K. Gaillard]] and [[Benjamin W. Lee]] in 1974 to be less than {{val|5|u=GeV/c2}}.<ref>Giudice, Gian Francesco. "Naturally speaking: the naturalness criterion and physics at the LHC". Perspectives on LHC physics (2008): 155–178.</ref>{{sfn|Gaillard|Lee|1974}}