Short answers, pulled from the story.
The tau particle is an elementary lepton with a negative electric charge and a spin of one-half, similar to the electron but with a far greater mass. Because of that extra mass, the tau can decay into hadrons, something no electron can do, and it is potentially more penetrating than an electron due to lower bremsstrahlung emission.
Martin Lewis Perl, working with colleagues at the Stanford Linear Accelerator Center and Lawrence Berkeley National Laboratory, detected the tau in a series of experiments between 1974 and 1977. The theoretical groundwork was laid independently by Yung-su Tsai in a 1971 article.
Martin Lewis Perl shared the 1995 Nobel Prize in Physics for the experimental discovery of the tau lepton. He shared the prize with Frederick Reines, who was honored for his separate discovery of the electron neutrino.
The tau lepton has a lifetime of 2.9 units (expressed in the standard short scientific notation) and a mass significantly greater than both the electron and the muon. Because its lifetime is so short, its range in matter is set by its decay length rather than by radiation losses.
The tau decays hadronically about 64.79 percent of the time through the weak interaction. Its largest single decay channel, at roughly 25.49 percent, produces a charged pion, a neutral pion, and a tau neutrino. It also decays leptonically into an electron about 17.82 percent of the time and into a muon about 17.39 percent of the time.
Tau exotic atoms are predicted bound states formed when a tau or antitau combines electromagnetically with another charged particle, including a state called tauonium made of a tau and an antitau. As of 2022, none of these exotic atoms have been observed; detecting one would provide a test of quantum electrodynamics.