Z particle. Smaller than protons and electrons.
did you just call me?
Child: A Lepton
the hell is that?
Child: You wouldn't understand.
Woman: No, speak
Child: A lepton is a Z particle.
Child: Do you know what
protons and electrons are?
Child: OK, what
Woman: They're those teeny tiny things atoms are made
Child: Well, leptons are even smaller.
(Shakta - Lepton Head Pt. III)