Neutral Pion (π⁰)

Neutral partner of the charged pions, decaying electromagnetically to two photons almost instantly.

Core Principles & Analysis

• Lives about 8.5 × 10⁻¹⁷ seconds — orders of magnitude shorter than its charged siblings.
• Decays to two photons about 98.8% of the time.
• Its measured decay rate gave early evidence that quarks come in three colors.

Specifications & Metrics

• SPIN: 0
• SYMBOL: π⁰
• CHARGE: 0 (neutral)
• MASS: 134.9768 ± 5 × 10⁻⁴ MeV/c²
• MEAN LIFE: 8.43 × 10⁻¹⁷ ± 1.3 × 10⁻¹⁸ s
• PDG ID: S009
• PDG EDITION: PDG 2026

Principal Decay Modes

• pi0 → 2gamma — 98.823 ± 0.034%
• pi0 → e+ e- gamma — 1.174 ± 0.035%
• pi0 → gamma positronium — 0.000000182 ± 0.000000029%
• pi0 → e+ e+ e- e- — 0.00334 ± 0.00016%
• pi0 → e+ e- — 0.00000646 ± 0.00000033%

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

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