by the inability to conserve energy and momentum with only one. However, no other muons, electrons, photons, or hadrons were detected. It was proposed that this event was the production and subsequent decay of a new particle pair: This was difficult to verify, because the energy to produce the pair is similar to the threshold for D meson production. The mass and spin of the tau was subsequently established by work done at DESY-Hamburg with the Double Arm Spectrometer (DASP), and at SLAC-Stanford with the SPEAR Direct Electron Counter (DELCO), The symbol was derived from the Greek (triton, meaning "third" in English), since it was the third charged lepton discovered. Martin Lewis 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. Tau decay The tau is the only lepton that can decay into hadrons – the masses of other leptons are too small. Like the leptonic decay modes of the tau, the hadronic decay is through the weak interaction. The branching fractions of the dominant hadronic tau decays are: 25.49% for decay into a charged pion, a neutral pion, and a tau neutrino; 10.82% for decay into a charged pion and a tau neutrino; 9.26% for decay into a charged pion, two neutral pions, and a tau neutrino; 8.99% for decay into three charged pions (of which two have the same electrical charge) and a tau neutrino; 2.74% for decay into three charged pions (of which two have the same electrical charge), a neutral pion, and a tau neutrino; 1.04% for decay into three neutral pions, a charged pion, and a tau neutrino. In total, the tau lepton will decay hadronically approximately 64.79% of the time. The branching fractions of the common purely leptonic tau decays are: 17.82% for decay into a tau neutrino, electron and electron antineutrino; 17.39% for decay into a tau neutrino, muon, and muon antineutrino. The similarity of values of the two branching fractions is a consequence of lepton universality. Exotic atoms The tau lepton is predicted to form exotic atoms like other charged subatomic particles. One of such, consists of an antitauon and an electron: . Another one is an onium atom called true tauonium and is difficult to detect due to tau's extremely short lifetime at low (non-relativistic) energies needed to form this atom. Its detection would