Proton

Stable subatomic composite particle bound by strong force, composed of 2 up and 1 down quark.

Core Principles & Analysis

• Identified as a constituent of all atomic nuclei by Ernest Rutherford in 1919.
• Its charge radius of about 0.84 femtometers was pinned down by muonic hydrogen spectroscopy.
• Super-Kamiokande has never observed proton decay, setting lifetime limits beyond 10³⁴ years.

Specifications & Metrics

• MASS: 938.27208943 ± 2.9 × 10⁻⁷ MeV/c²
• SPIN: 1/2
• SYMBOL: p⁺
• PDG ID: S016
• PDG EDITION: PDG 2026
• CHARGE: +1 e

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