NationMaster - Encyclopedia: Strangeness

In particle physics, strangeness, denoted as

S

, is a property of particles, expressed as a quantum number for describing decay of particles in strong and electro-magnetic reactions, which occur in a short period of time. The strangeness of a particle is defined as: CPT-symmetry is a fundamental symmetry of physical laws under transformations that involve the inversions of charge, parity and time simultaneously. ... In the standard model of particle physics the Cabibbo Kobayashi Maskawa matrix (CKM matrix, sometimes earlier called KM matrix) is a unitary matrix which contains information on the strength of flavour changing weak decays. ... CP is the product of two symmetries: C for charge conjugation, which transforms a particle into its antiparticle, and P for parity, which creates the mirror image of a physical system. ... A phenomenon is said to be chiral if it is not identical to its mirror image (see Chirality (mathematics)). The spin of a particle may be used to define a handedness for that particle. ... Thousands of particles explode from the collision point of two relativistic (100 GeV per ion) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... A quantum number describes the energies of electrons in atoms. ... The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). ... Electromagnetic interaction is a fundamental force of nature and is felt by charged leptons and quarks. ...

where $N_{overline{s}}$ represents the number of strange anti-quarks ( ${overline{s}}$ ) and $N_s$ represents the number of strange quarks.

The derivation of the phrase "strange" or "strangeness" precedes the discovery of the quark, and was adopted after its discovery in order to preserve the continuity of the phrase; strangeness of anti-particles being referred to as +1, and particles as -1 as per the original definition. For all the quark flavor quantum numbers (strangeness, charm, topness and bottomness) the convention is that the flavor charge and the electric charge of a quark have the same sign. With this, any flavor carried by a charged meson has the same sign as its charge. Charm is the number of charm quarks (c) minus the number of charm anti-quarks () that are present in a particle: This makes charm quark to have a charm of +1 and anti-charm quark to have a charm of −1 (the charm sign agreeing with the quark charge... Topness (formerly also called Truth) quantum number is the number of top quarks (t) minus the number of top anti-quarks () that are present in a particle: Top quarks have a topness of +1 and anti-top quarks have a topness of −1. ... In Physics, Bottomness (also formerly called Beauty) quantum number is the number of bottom anti-quarks () minus the number of bottom quarks (b) that are present in a particle: Bottom quarks have a bottomness of −1 and bottom anti-quarks of +1, so the bottomness sign agrees with its... Mesons of spin 1 form a nonet In particle physics, a meson is a strongly interacting boson, that is, it is a hadron with integral spin. ...

Strangeness conservation

Strangeness was introduced, by Murray Gell-Mann and Kazuhiko Nishijima, originally to explain the fact that certain particles, such as the kaons or certain hyperons were created easily in particle collisions, yet decayed much slower than expected for their large masses and large production cross sections. Noting that collisions seemed to always produce pairs of these particles, it was postulated that a new conserved quality, dubbed "strangeness", was preserved during their creation, but not conserved in their decay. Murray Gell-Mann (born September 15, 1929 in Manhattan, New York City, USA) is an American physicist who received the 1969 Nobel Prize in physics for his work on the theory of elementary particles. ... In particle physics, Kaons (also called K-mesons and denoted K) are a group of four mesons distinguished by the fact that they carry a quantum number called strangeness. ... In particle physics, a hyperon is any subatomic particle which is a baryon (and hence a hadron and a fermion) with non-zero strangeness, but with zero charm and zero bottomness. ... In nuclear and particle physics, the concept of a cross section is used to express the likelihood of interaction between particles. ...

In our modern understanding, strangeness is conserved during the strong and the electromagnetic interaction, but not during the weak interactions. Consequently the lightest particles containing a strange quark cannot decay by the strong interaction, and must instead decay via the much slower weak interaction. In most cases change these decays change the value of the strangeness by one unit. However, this doesn't necessarily hold in second-order, weak reactions, where there are mixes of ${K}^0$ and $overline{K}^0$ mesons. The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). ... Electromagnetic interaction is a fundamental force of nature and is felt by charged leptons and quarks. ... The weak nuclear force or weak interaction is one of the four fundamental forces of nature. ...

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See also

Strangeness conservation