Strangeness

Strangeness is a quantum number assigned to hadrons containing strange quarks. Strong and electromagnetic interactions conserve it, while weak interactions can change it.

Strange quark: A quark of the second generation with electric charge −1/3 and strangeness −1. Each strange quark contributes −1 to a hadron’s strangeness.
Strong interaction: The fundamental interaction that binds quarks into hadrons and acts on color charge. It conserves strangeness, constraining which hadron reactions can occur.
Kaon: A meson containing one strange or antistrange quark and one up- or down-type quark. Kaons were among the puzzling particles whose unusual lifetimes prompted the strangeness idea.
Gell-Mann–Nishijima formula: A relation connecting electric charge, isospin, baryon number, and strangeness for hadrons. It lets strangeness contribute directly to predicting a hadron’s electric charge.
Quark model: A model describing hadrons as bound states of quarks. It provides the quark-content bookkeeping used to assign hadron strangeness.
Electromagnetic interaction: The fundamental interaction between particles carrying electric charge. It also conserves strangeness, unlike the weak interaction.
Lambda baryon: A baryon containing one up, one down, and one strange quark. The Lambda’s production and decay helped reveal the pattern later described by strangeness.
Particle Data Group: An international collaboration that reviews and publishes measurements of particle properties. Its particle listings report strangeness as a standard hadron quantum number.
Hadron: A composite particle made of quarks held together by the strong interaction. Strangeness is assigned to hadrons according to their strange-quark content.
Weak interaction: The fundamental interaction responsible for processes such as beta decay and flavor-changing particle transitions. It can change strangeness, enabling strange hadrons to decay.

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