Definition:
Strangeness is a quantum number used in particle physics to describe a property of subatomic particles, particularly hadrons, that is conserved in strong and electromagnetic interactions but not in weak interactions.
Overview:
Strangeness was introduced in the 1950s to explain the unexpectedly long lifetimes of certain particles, such as kaons and hyperons, which were produced rapidly via the strong force but decayed slowly via the weak force. This behavior indicated that a new conserved quantity was at play during production but could change during decay. The concept became integral to the development of the quark model, where strangeness is associated with the presence of strange quarks (s quarks) or strange antiquarks (s̄ quarks) within a particle.
Etymology/Origin:
The term "strangeness" was coined by physicist Murray Gell-Mann in 1953, derived from the observation that certain particles exhibited "strange" behavior—specifically, their prolonged lifetimes compared to typical strongly interacting particles. Gell-Mann introduced the strangeness quantum number to formalize this property.
Characteristics:
- Strangeness (symbol: S) is defined as S = −(ns − n̄s), where ns is the number of strange quarks and n̄s is the number of strange antiquarks in a particle.
- It is conserved in strong and electromagnetic interactions, meaning the total strangeness before and after such reactions remains constant.
- It is not conserved in weak interactions, allowing particles with nonzero strangeness to decay into lower-mass, non-strange particles over time.
- Examples: A kaon (K⁺), composed of an up quark and a strange antiquark (ūs), has a strangeness of +1. A lambda baryon (Λ⁰), containing up, down, and strange quarks (uds), has a strangeness of −1.
- Strangeness plays a role in the classification of hadrons in the Eightfold Way, a precursor to the quark model.
Related Topics:
- Quantum numbers
- Quark model
- Hadrons (baryons and mesons)
- Weak interaction
- Conservation laws in physics
- Eightfold Way
- Kaons, hyperons, and other strange particles
- Standard Model of particle physics