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 nucleus, atomic nuclei ...

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. The Standard Model presently recognizes seventeen distinct particles—twelve fermions and five bosons. As a c ...

. Strange quarks are found in

subatomic particle In physics, a subatomic particle is a particle smaller than 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 baryon, lik ...

s called

hadron In particle physics, a hadron is a composite subatomic particle made of two or more quarks held together by the strong nuclear force. Pronounced , the name is derived . They are analogous to molecules, which are held together by the electri ...

s. Examples of hadrons containing strange quarks include

kaon In particle physics, a kaon, also called a K meson and denoted , is any of a group of four mesons distinguished by a quantum number called strangeness. In the quark model they are understood to be bound states of a strange quark (or antiquark ...

s (), strange D mesons (), Sigma baryons (), and other strange particles. 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 (but also the other three remaining quarks) 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 is an elementary particle found in composite subatomic particles called hadrons such as the J/psi meson and the charmed baryons created in particle accelerator collisions. Several bosons, including th ...

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

electric charge Electric charge (symbol ''q'', sometimes ''Q'') is a physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be ''positive'' or ''negative''. Like charges repel each other and ...

of ''e'' and a bare mass of . Like all

s, the strange quark is an elementary

fermion In particle physics, a fermion is a subatomic particle that follows Fermi–Dirac statistics. Fermions have a half-integer spin (spin 1/2, spin , Spin (physics)#Higher spins, spin , etc.) and obey the Pauli exclusion principle. These particles i ...

with spin , and experiences all four

fundamental interaction In physics, the fundamental interactions or fundamental forces are interactions in nature that appear not to be reducible to more basic interactions. There are four fundamental interactions known to exist: * gravity * electromagnetism * weak int ...

gravitation In physics, gravity (), also known as gravitation or a gravitational interaction, is a fundamental interaction, a mutual attraction between all massive particles. On Earth, gravity takes a slightly different meaning: the observed force b ...

electromagnetism In physics, electromagnetism is an interaction that occurs between particles with electric charge via electromagnetic fields. The electromagnetic force is one of the four fundamental forces of nature. It is the dominant force in the interacti ...

weak interaction In nuclear physics and particle physics, the weak interaction, weak force or the weak nuclear force, is one of the four known fundamental interactions, with the others being electromagnetism, the strong interaction, and gravitation. It is th ...

s, and

strong interaction In nuclear physics and particle physics, the strong interaction, also called the strong force or strong nuclear force, is one of the four known fundamental interaction, fundamental interactions. It confines Quark, quarks into proton, protons, n ...

s. The

antiparticle In particle physics, every type of particle of "ordinary" matter (as opposed to antimatter) is associated with an antiparticle with the same mass but with opposite physical charges (such as electric charge). For example, the antiparticle of the ...

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 by

George Rochester George Dixon Rochester, Fellow of the Royal Society, FRS (4 February 1908 – 26 December 2001) was a England, British physicist known for having co-discovered, with Sir Clifford Charles Butler, a subatomic particle called the kaon. Biography ...

and Clifford Butler in Department of Physics and Astronomy, University of Manchester in 1947 (

s), with the existence of the strange quark itself (and that of the up and

down quark The down quark (symbol: d) is a type of elementary particle, and a major constituent of matter. The down quark is the second-lightest of all quarks, and combines with other quarks to form composite particles called hadrons. Down quarks are most ...

s) postulated in 1964 by

Murray Gell-Mann Murray Gell-Mann (; September 15, 1929 – May 24, 2019) was an American theoretical physicist who played a preeminent role in the development of the theory of elementary particles. Gell-Mann introduced the concept of quarks as the funda ...

and

George Zweig George Zweig (; born May 30, 1937) is an American physicist of Russian-Jewish origin. 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"). ...

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 SLAC National Accelerator Laboratory, originally named the Stanford Linear Accelerator Center, is a Federally funded research and development centers, federally funded research and development center in Menlo Park, California, Menlo Park, Ca ...

. 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 , Hydron (chemistry), H+, or 1H+ with a positive electric charge of +1 ''e'' (elementary charge). Its mass is slightly less than the mass of a neutron and approximately times the mass of an e ...

neutron The neutron is a subatomic particle, symbol or , that has no electric charge, and a mass slightly greater than that of a proton. The Discovery of the neutron, neutron was discovered by James Chadwick in 1932, leading to the discovery of nucle ...

s and

pion In particle physics, a pion (, ) or pi meson, denoted with the Greek alphabet, Greek letter pi (letter), pi (), is any of three subatomic particles: , , and . Each pion consists of a quark and an antiquark and is therefore a meson. Pions are the ...

s were thought to be

s. However, new hadrons were discovered and the " particle zoo" 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 lifetimes of around 10⁻²³ seconds. When they decayed through the

s, they had lifetimes of around 10⁻¹⁰ seconds. While studying these decays,

(in 1953) and Kazuhiko Nishijima (in 1955) developed the concept of '' strangeness'' (which Nishijima called ''eta-charge'', after the eta meson ()) 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 independently proposed a hadron classification scheme called the eightfold way, also known as

SU(3) In mathematics, the special unitary group of degree , denoted , is the Lie group of unitary matrices with determinant 1. The matrices of the more general unitary group may have complex determinants with absolute value 1, rather than real 1 i ...

flavor symmetry. 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 that give rise to the quantum numbers of the hadrons. The quark model underlies "flavor SU(3)", or the Eig ...

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

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

History

See also

References

Further reading