Strange quark

The strange quark, or s quark, is a fundamental building block of our universe. It is an elementary particle, which means it is not made of anything smaller. Scientists classify it as the third lightest of all known quarks. These quarks are found inside larger subatomic particles known as hadrons.

Strange quarks are essential to understanding the second generation of matter. This group of matter also includes the charm quark. By studying these particles, scientists can learn how the smallest parts of nature behave.

Every strange quark possesses specific physical properties that define its behavior. It carries an electric charge of -1/3. Its bare mass is measured at approximately 95 MeV/c². As an elementary fermion, it also has a spin of 1/2. The strange quark experiences all four fundamental interactions in physics. These include gravitation, electromagnetism, the weak interaction, and the strong interaction.

There is also an antiparticle called the strange antiquark. This particle has properties with the same magnitude but the opposite sign.

Strange quarks exist within several different types of hadrons. One common example is the kaon, which was the first strange particle discovered. They are also found in strange D mesons. Another type of particle that contains them is the sigma baryon.

Scientists use these different hadrons to study how quarks interact. The way these particles are built helps researchers understand the structure of matter. Each type of hadron shows a different way that quarks can combine.

In the early 20th century, the understanding of particles was very different. Scientists originally thought that protons, neutrons, and pions were elementary particles. However, the discovery of new particles created a "particle zoo." By the 1950s, researchers had found dozens of different particles. Some particles decayed very quickly through the strong interaction. These had lifetimes of about 10⁻²³ seconds. Others lived longer by decaying through weak interactions.

These longer-lived particles had lifetimes of about 10⁻¹⁰ seconds.

To explain these differences, scientists developed new theories about "strangeness." In 1953, Murray Gell-Mann began working on this concept. In 1955, Kazuhiko Nishijima developed the idea of strangeness, which he called eta-charge. They created the Gell-Mann–Nishijima formula to understand strange decays. Later, in 1961, Gell-Mann and Yuval Ne'eman proposed the eightfold way. This was a classification scheme known as SU(3) flavor symmetry. It helped order hadrons into specific groups called isospin multiplets.

The actual existence of quarks was proposed in 1964. Murray Gell-Mann and George Zweig independently suggested the quark model. At that time, the model only included up, down, and strange quarks. They explained that up and down quarks carried isospin. The strange quark was the carrier of strangeness.

While the model was helpful, it lacked direct physical evidence for many years. It took further experimentation to prove that these tiny particles were real.

Direct evidence finally arrived in 1968 at the Stanford Linear Accelerator Center. Scientists performed experiments using a method called deep inelastic scattering. These tests showed that protons actually had an internal substructure. The data suggested that protons were made of three more fundamental particles. This confirmed the existence of up and down quarks. It also confirmed the existence of strange quarks through the eightfold way.

While some scientists preferred Richard Feynman's "parton" description, the quark theory eventually became the accepted standard.