Animated particle tracks showing the production and decay of tau leptons. The ALEPH detector is shown in cross-section. ALEPH was a detector on the LEP at CERN, the particle physics lab near Geneva. An electron and a positron were accelerated to high energy and annihilate at centre, creating a Z boson which rapidly decays into a tau-plus and a tau-minus particle pair. The Z and the taus live too briefly to be seen, but the taus are revealed by their characteristic 3+3 decay into two back-to-back sets of three pions (coloured tracks). The tau is a lepton, a heavy version of the electron and muon.