The strange quark or s quark (from its symbol, s) is the third lightest of all

quark A quark () is a type of elementary particle and a fundamental constituent of matter. Quarks combine to form composite particles called hadrons, the most stable of which are protons and neutrons, the components of atomic nuclei. All commonly o ...

s, a type of elementary particle. Strange quarks are found in

subatomic particle In physical sciences, a subatomic particle is a particle that composes an atom. According to the Standard Model of particle physics, a subatomic particle can be either a composite particle, which is composed of other particles (for example, a prot ...

s called

hadron In particle physics, a hadron (; grc, ἁδρός, hadrós; "stout, thick") is a composite subatomic particle made of two or more quarks held together by the strong interaction. They are analogous to molecules that are held together by the e ...

s. Examples of hadrons containing strange quarks include kaons (), strange D mesons (),

Sigma baryon Sigma (; uppercase Σ, lowercase σ, lowercase in word-final position ς; grc-gre, σίγμα) is the eighteenth letter of the Greek alphabet. In the system of Greek numerals, it has a value of 200. In general mathematics, uppercase Σ is used ...

s (), and other

strange particle A strange particle is an elementary particle with a strangeness quantum number different from zero. Strange particles are members of a large family of elementary particles carrying the quantum number of strangeness, including several cases where the ...

s. According to the IUPAP, the symbol s is the official name, while "strange" is to be considered only as a mnemonic. The name sideways has also been used because the s quark has an I value of 0 while the u ("up") and d ("down") quarks have values of + and − respectively. Along with the

charm quark The charm quark, charmed quark or c quark (from its symbol, c) is the third-most massive of all quarks, a type of elementary particle. Charm quarks are found in hadrons, which are subatomic particles made of quarks. Examples of hadrons containin ...

, it is part of the second generation of matter. It has an electric charge of − ''e'' and a

bare mass In quantum field theory, specifically the theory of renormalization, the bare mass of an elementary particle is the limit of its mass as the scale of distance approaches zero or, equivalently, as the energy of a particle collision approaches infini ...

of . Like all

s, the strange quark is an elementary

fermion In particle physics, a fermion is a particle that follows Fermi–Dirac statistics. Generally, it has a half-odd-integer spin: spin , spin , etc. In addition, these particles obey the Pauli exclusion principle. Fermions include all quarks and ...

with

spin Spin or spinning most often refers to: * Spinning (textiles), the creation of yarn or thread by twisting fibers together, traditionally by hand spinning * Spin, the rotation of an object around a central axis * Spin (propaganda), an intentionally b ...

, and experiences all four fundamental interactions: gravitation,

electromagnetism In physics, electromagnetism is an interaction that occurs between particles with electric charge. It is the second-strongest of the four fundamental interactions, after the strong force, and it is the dominant force in the interactions of ...

weak interaction In nuclear physics and particle physics, the weak interaction, which is also often called the weak force or weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction ...

s, and

strong interaction The strong interaction or strong force is a fundamental interaction that confines quarks into proton, neutron, and other hadron particles. The strong interaction also binds neutrons and protons to create atomic nuclei, where it is called the ...

s. The

antiparticle In particle physics, every type of particle is associated with an antiparticle with the same mass but with opposite physical charges (such as electric charge). For example, the antiparticle of the electron is the positron (also known as an antie ...

of the strange quark is the strange antiquark (sometimes called ''antistrange quark'' or simply ''antistrange''), which differs from it only in that some of its properties have equal magnitude but opposite sign. The first

(a particle containing a strange quark) was discovered in 1947 ( kaons), but the existence of the strange quark itself (and that of the up and

down quark The down quark or d quark (symbol: d) is the second-lightest of all quarks, a type of elementary particle, and a major constituent of matter. Together with the up quark, it forms the neutrons (one up quark, two down quarks) and protons (two up ...

s) was only postulated in 1964 by Murray Gell-Mann and

George Zweig George Zweig (; born May 30, 1937) is a Russian-American physicist. He was trained as a particle physicist under Richard Feynman. He introduced, independently of Murray Gell-Mann, the quark model (although he named it "aces"). He later turned his ...

to explain the '' eightfold way'' classification scheme of

s. The first evidence for the existence of quarks came in 1968, in deep inelastic scattering experiments at the Stanford Linear Accelerator Center. These experiments confirmed the existence of up and down quarks, and by extension, strange quarks, as they were required to explain the ''eightfold way''.

History

In the beginnings of particle physics (first half of the 20th century),

s such as protons, neutrons and pions were thought to be elementary particles. However, new hadrons were discovered and the "

particle zoo In particle physics, the term particle zoo is used colloquially to describe the relatively extensive list of known subatomic particles by comparison to the variety of species in a zoo. In the history of particle physics, the topic of particles was ...

" grew from a few particles in the early 1930s and 1940s to several dozens of them in the 1950s. Some particles were much longer lived than others; most particles decayed through the

and had

lifetime Lifetime may refer to: * Life expectancy, the length of time a person is expected to remain alive Arts, entertainment, and media Music * Lifetime (band), a rock band from New Jersey * ''Life Time'' (Rollins Band album), by Rollins Band * ...

s of around 10⁻²³ seconds. When they decayed through the

s, they had lifetimes of around 10⁻¹⁰ seconds. While studying these decays, Murray Gell-Mann (in 1953) and

Kazuhiko Nishijima (4 October 1926 – 15 February 2009) was a Japanese physicist who made significant contributions to particle physics. He was professor emeritus at the University of Tokyo and Kyoto University until his death in 2009. He was born in Tsuchiura ...

(in 1955) developed the concept of '' strangeness'' (which Nishijima called ''eta-charge'', after the

eta meson The eta () and eta prime meson () are isosinglet mesons made of a mixture of up, down and strange quarks and their antiquarks. The charmed eta meson () and bottom eta meson () are similar forms of quarkonium; they have the same spin and pari ...

()) to explain the "strangeness" of the longer-lived particles. The

Gell-Mann–Nishijima formula The Gell-Mann–Nishijima formula (sometimes known as the NNG formula) relates the baryon number ''B'', the strangeness ''S'', the isospin ''I3'' of quarks and hadrons to the electric charge ''Q''. It was originally given by Kazuhiko Nishijima an ...

is the result of these efforts to understand strange decays. Despite their work, the relationships between each particle and the physical basis behind the strangeness property remained unclear. In 1961, Gell-Mann and

Yuval Ne'eman Yuval Ne'eman ( he, יובל נאמן, 14 May 1925 – 26 April 2006) was an Israeli theoretical physicist, military scientist, and politician. He was Minister of Science and Development in the 1980s and early 1990s. He was the President o ...

independently proposed a hadron classification scheme called the eightfold way, also known as SU(3)

flavor symmetry In particle physics, flavour or flavor refers to the ''species'' of an elementary particle. The Standard Model counts six flavours of quarks and six flavours of leptons. They are conventionally parameterized with ''flavour quantum numbers'' th ...

. This ordered hadrons into isospin multiplets. The physical basis behind both isospin and strangeness was only explained in 1964, when Gell-Mann and

independently proposed the

quark model In particle physics, the quark model is a classification scheme for hadrons in terms of their valence quarks—the quarks and antiquarks which give rise to the quantum numbers of the hadrons. The quark model underlies "flavor SU(3)", or the Ei ...

, which at that time consisted only of the up, down, and strange quarks. Up and down quarks were the carriers of isospin, while the strange quark carried strangeness. While the quark model explained the ''eightfold way'', no direct evidence of the existence of quarks was found until 1968 at the Stanford Linear Accelerator Center. Deep inelastic scattering experiments indicated that protons had substructure, and that protons made of three more-fundamental particles explained the data (thus confirming the

). At first people were reluctant to identify the three-bodies as quarks, instead preferring

Richard Feynman Richard Phillips Feynman (; May 11, 1918 – February 15, 1988) was an American theoretical physicist, known for his work in the path integral formulation of quantum mechanics, the theory of quantum electrodynamics, the physics of the superfl ...

's parton description, but over time the quark theory became accepted (see '' November Revolution'').

History

See also

References

Further reading