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 In particle physics, an elementary particle or fundamental particle is a subatomic particle that is not composed of other particles. Particles currently thought to be elementary include electrons, the fundamental fermions ( quarks, leptons, an ...

. 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 pr ...

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 ele ...

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

strange D meson The D mesons are the lightest particle containing charm quarks. They are often studied to gain knowledge on the weak interaction. The strange D mesons (Ds) were called "F mesons" prior to 1986. Overview The D mesons were discover ...

s (), Sigma baryons (), and other strange particles. According to the

IUPAP The International Union of Pure and Applied Physics (IUPAP ) is an international non-governmental organization whose mission is to assist in the worldwide development of physics, to foster international cooperation in physics, and to help in the ...

, 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, it is part of the second generation of matter. It has an

electric charge Electric charge is the physical property of matter that causes charged matter to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative'' (commonly carried by protons and electrons respe ...

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 infin ...

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 an ...

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 In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the stron ...

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 a ...

, weak interactions, 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 n ...

s. The antiparticle 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 strange particle (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 quarks) was only postulated in 1964 by Murray Gell-Mann and George Zweig to explain the '' eightfold way'' classification scheme of

s. The first evidence for the existence of quarks came in 1968, in

deep inelastic scattering Deep inelastic scattering is the name given to a process used to probe the insides of hadrons (particularly the baryons, such as protons and neutrons), using electrons, muons and neutrinos. It provided the first convincing evidence of the reality ...

experiments at the

Stanford Linear Accelerator Center SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center, is a United States Department of Energy National Laboratory operated by Stanford University under the programmatic direction of the U.S. Departme ...

. 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

proton A proton is a stable subatomic particle, symbol , H+, or 1H+ with a positive electric charge of +1 ''e'' elementary charge. Its mass is slightly less than that of a neutron and 1,836 times the mass of an electron (the proton–electron mass ...

neutron The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons beh ...

s and pions were thought to be

s. 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 wa ...

" 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 weak interactions, they had lifetimes of around 10⁻¹⁰ seconds. While studying these decays, Murray Gell-Mann (in 1953) and Kazuhiko Nishijima (in 1955) developed the concept of ''

strangeness In particle physics, strangeness ("''S''") is a property of particles, expressed as a quantum number, for describing decay of particles in strong and electromagnetic interactions which occur in a short period of time. The strangeness of a parti ...

'' (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 p ...

()) to explain the "strangeness" of the longer-lived particles. The Gell-Mann–Nishijima formula 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 George Zweig 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 E ...

, 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

Deep inelastic scattering Deep inelastic scattering is the name given to a process used to probe the insides of hadrons (particularly the baryons, such as protons and neutrons), using electrons, muons and neutrinos. It provided the first convincing evidence of the reality ...

experiments indicated that

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

History

See also

References

Further reading