In the realm of particle physics, "strangeness" refers to a quantum number associated with certain types of subatomic particles. The concept of strangeness was introduced in the mid-20th century to explain the behavior of particles known as strange particles.
Strangeness is a property that helps identify and classify particles based on their interactions through the strong and weak nuclear forces. It is quantified by an integer value called the "strangeness quantum number" (S). Particles that have a non-zero strangeness are called strange particles.
The strangeness quantum number is conserved in strong and electromagnetic interactions but can change in weak interactions. When a strange particle decays weakly, the total strangeness of the decay products must remain the same as the initial strangeness of the particle.
Strange particles are characterized by containing strange quarks or antiquarks. For example, the kaon (K) and lambda (Λ) particles are strange particles. They have a strangeness value of -1 and -1, respectively. Antiparticles of strange particles have a strangeness of +1.
The concept of strangeness played a significant role in the development of the quark model, which provides a framework for understanding the structure of subatomic particles. Strangeness was later unified with other properties in the theory of quantum chromodynamics (QCD), which describes the strong interactions between quarks and the behavior of particles within the framework of the Standard Model of particle physics.