You discovered the Tau lepton.
The tau is an elementary particle similar to the electron, with negative electric charge and a spin of 1/2. Together with the electron, the muon, and the three neutrinos, it is classified as a lepton. Despite of the meaning of the word lepton (fine, small, thin) the tau is very massive: it has mass of 1776.82 MeV/c^2 (for comparison: the mass of the electron is 0.511 MeV/c^2, the mass of the proton is 938.27 MeV/c^2).
The tau was detected in a series of experiments between 1974 and 1977 by Martin Lewis Perl with his colleagues at the SLAC-LBL group. Their equipment consisted of SLAC's then-new e+āeā colliding ring, called SPEAR, and the LBL magnetic detector. They could detect and distinguish between leptons, hadrons and photons.
Martin Perl shared the 1995 Nobel Prize in Physics with Frederick Reines. The latter was awarded his share of the prize for experimental discovery of the neutrino.