Tauon

The tauon is a type of lepton found when electrons and positrons collide at high energies. It is 17 times as massive as a muon and 3500 times more massive than an electron, lasting less than five trillionth of a second before breaking down into a muon.
 Martin L. Perl United States 1974 Tauon

The tauon is a type of lepton found when electrons and positrons collide at high energies. It is 17 times as massive as a muon and 3500 times more massive than an electron, lasting less than five trillionth of a second before breaking down into a muon.