Editing Lepton (section)

== Etymology ==
The name ''lepton'' comes from the [[Ancient Greek|Greek]] {{lang|el|λεπτός}} ''leptós'', "fine, small, thin" ([[Grammatical gender|neuter]] nominative/accusative singular form: λεπτόν ''leptón'');<ref>[http://www.etymonline.com/index.php?term=lepton "lepton"]. ''[[Online Etymology Dictionary]]''.</ref><ref>{{LSJ|lepto/s|λεπτός|ref}}.</ref> the earliest attested form of the word is the [[Mycenaean Greek]] {{lang|gmy|𐀩𐀡𐀵}}, ''re-po-to'', written in [[Linear B]] syllabic script.<ref>Found on the [[Knossos|KN]] L 693 and [[Pylos|PY]] Un 1322 tablets. {{cite web|title=The Linear B word re-po-to|publisher=Palaeolexicon. Word study tool of ancient languages|url=http://www.palaeolexicon.com/ShowWord.aspx?Id=16917}} {{cite web|url=http://minoan.deaditerranean.com/resources/linear-b-sign-groups/re/re-po-to/|title=re-po-to|work=Minoan Linear A & Mycenaean Linear B|last=Raymoure|first=K.A.|publisher=Deaditerranean|access-date=2014-03-22|archive-date=2016-01-16|archive-url=https://web.archive.org/web/20160116072258/http://minoan.deaditerranean.com/resources/linear-b-sign-groups/re/re-po-to/|url-status=dead}} {{cite web|title=KN 693 L (103)|url=https://www2.hf.uio.no/damos/Index/item/chosen_item_id/630}} {{cite web|title=PY 1322 Un + fr. (Cii)|website=DĀMOS: Database of Mycenaean at Oslo|url=https://www2.hf.uio.no/damos/Index/item/chosen_item_id/5021|publisher=[[University of Oslo]]}}</ref> ''Lepton'' was first used by physicist [[Léon Rosenfeld]] in 1948:<ref>{{harvnb|Rosenfeld|1948}}</ref>
<blockquote>Following a suggestion of Prof. [[C. Møller]], I adopt—as a pendant to "nucleon"—the denomination "lepton" (from λεπτός, small, thin, delicate) to denote a particle of small mass.</blockquote>

Rosenfeld chose the name as the common name for electrons and (then hypothesized) neutrinos. Additionally, the muon, initially classified as a meson, was reclassified as a lepton in the 1950s. The masses of those particles are small compared to nucleons—the mass of an electron ({{val|0.511|ul=MeV/c2}})<ref name="Electron">{{harvnb|Amsler|2008}}: [http://pdg.lbl.gov/2008/listings/s003.pdf Particle listings—{{SubatomicParticle|Electron-}}]</ref> and the mass of a muon (with a value of {{val|105.7|u=MeV/c2}})<ref name="Muon">{{harvnb|Amsler|2008}}: [http://pdg.lbl.gov/2008/listings/s004.pdf Particle listings—{{SubatomicParticle|Muon-}}]</ref> are fractions of the mass of the "heavy" proton ({{val|938.3|u=MeV/c2}}), and the mass of a neutrino is nearly zero.<ref name="Proton">{{harvnb|Amsler|2008}}: [http://pdg.lbl.gov/2008/listings/s016.pdf Particle listings—{{SubatomicParticle|Proton+}}]</ref> However, the mass of the tau (discovered in the mid-1970s) ({{val|1777|u=MeV/c2}})<ref name="Tauon">{{harvnb|Amsler|2008}}: [http://pdg.lbl.gov/2008/listings/s035.pdf Particle listings—{{SubatomicParticle|Tau-}}]</ref> is nearly twice that of the proton and {{physconst|mtau/me|round=0}} times that of the electron.