Lepton number
A conserved quantum number assigned to leptons and their interactions. Electrons and electron neutrinos have lepton number +1; positrons and electron antineutrinos have lepton number -1; all other particles have lepton number 0. Lepton number is conserved in all known interactions.
Formula
L = +1 (leptons), L = −1 (antileptons), L = 0 (baryons, photons)
Real World
In beta-minus decay inside a nuclear reactor, antineutrinos (L = −1) are produced alongside electrons (L = +1), keeping total lepton number at zero — these antineutrinos were first detected by Reines and Cowan at the Savannah River nuclear plant in 1956.
Exam Focus
Check electron lepton number and muon lepton number separately — they are independently conserved and mixing them up is a common exam error.
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