Tau Lepton

Heavy unstable elementary particle in the third generation of leptons.

Core Principles & Analysis

• Discovered by Martin Perl's team at SLAC between 1974 and 1977.
• The only lepton heavy enough to decay into hadrons, which it does about two-thirds of the time.
• Its mean lifetime is just 2.9 × 10⁻¹³ seconds.

Specifications & Metrics

• MASS: 1776.93 ± 0.09 MeV/c²
• SPIN: 1/2
• SYMBOL: τ⁻
• MEAN LIFE: 2.903 × 10⁻¹³ ± 5 × 10⁻¹⁶ s
• PDG ID: S035
• PDG EDITION: PDG 2026
• CHARGE: −1 e

Principal Decay Modes

• tau- → particle-≥0 neutrals ≥0K0 nu_tau (“1-prong”) — 85.24 ± 0.06%
• tau- → particle-≥0 neutrals ≥0K(L)0 nu_tau — 84.58 ± 0.06%
• tau- → mu- nubar_mu nu_tau — 17.37 ± 0.04%
• tau- → mu- nubar_mu nu_tau gamma — 0.367 ± 0.008%
• tau- → e- nubar_e nu_tau — 17.85 ± 0.04%

Branching fractions: Particle Data Group, 2026 edition (CC BY 4.0).

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