J/ψ Meson

Bound state of a charm quark and antiquark whose 1974 discovery confirmed a fourth quark flavor.

Core Principles & Analysis

• Found simultaneously in November 1974 by Ting’s Brookhaven team and Richter’s SLAC team — the "November Revolution".
• Its strikingly narrow width meant a long lifetime, explainable only by a new quantum number: charm.
• Ting and Richter shared the Nobel Prize just two years later, in 1976.

Specifications & Metrics

• SPIN: 1
• SYMBOL: J/ψ
• CHARGE: 0 (neutral)
• MASS: 3096.9 ± 0.006 MeV/c²
• PDG ID: M070
• PDG EDITION: PDG 2026

Principal Decay Modes

• J/psi(1S) → hadrons — 87.7 ± 0.5%
• J/psi(1S) → virtual gamma → hadrons — 13.46 ± 0.07%
• J/psi(1S) → g g g — 64.1 ± 1.0%
• J/psi(1S) → gamma g g — 8.8 ± 1.1%
• J/psi(1S) → e+ e- — 5.971 ± 0.032%

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

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