Z Boson

Neutral weak force mediator mediating neutral current interactions.

Core Principles & Analysis

• Discovered at CERN in 1983, months after the W boson.
• Precision measurements of its decay width at LEP showed exactly three light neutrino species exist.
• Neutral current interactions it mediates were first observed at the Gargamelle bubble chamber in 1973.

Specifications & Metrics

• MASS: 91.1879 ± 0.002 GeV/c²
• SPIN: 1
• SYMBOL: Z⁰
• DECAY WIDTH: 2.4955 ± 0.0023 GeV
• PDG ID: S044
• PDG EDITION: PDG 2026
• CHARGE: 0 (neutral)

Principal Decay Modes

• Z → e+ e- — 3.3632 ± 0.0042%
• Z → mu+ mu- — 3.3662 ± 0.0066%
• Z → tau+ tau- — 3.3696 ± 0.0083%
• Z → lepton+ lepton- — 3.3658 ± 0.0023%
• Z → lepton+ lepton- lepton+ lepton- — 0.000455 ± 0.000017%

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

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