strange quark

strange quark
Name	Strange quark
Generation	Second
Charge	−1/3 e
Mass	~95 MeV/c^2 (current)
Spin	1/2
Color	red, green, blue
Discovery	1947 (strangeness phenomena), 1964 (quark model)
Interactions	Electromagnetism, Weak interaction, Strong interaction

strange quark The strange quark is a fundamental fermion of the second generation, carrying a negative one-third elementary charge and participating in Strong interaction, Electromagnetism, and the Weak interaction. It contributes to the structure of many hadrons observed in experiments at facilities such as CERN, Fermilab, SLAC National Accelerator Laboratory, and KEK, and it plays a central role in theoretical frameworks developed by researchers including Murray Gell-Mann, George Zweig, and Yoichiro Nambu.

Overview

The strange quark appears in the Quark model and in the Standard Model as one of six flavors alongside up quark, down quark, charm quark, bottom quark, and top quark. Strange-containing hadrons, often called strange particles, were first identified in cosmic ray experiments and later produced in controlled environments at colliders such as Brookhaven National Laboratory, DESY, TRIUMF, and Institut Laue-Langevin. The concept of "strangeness" was introduced by theorists including Murray Gell-Mann and Kazuhiko Nishijima to account for production and decay patterns observed in experiments by physicists like C. F. Powell and Marietta Blau.

Properties

Intrinsic properties of the strange quark include its fractional electric charge, spin-1/2 fermionic nature consistent with the Dirac equation, and its participation in Quantum Chromodynamics via color charge. Measured parameters are refined through analyses by collaborations such as Particle Data Group and experiments at Large Hadron Collider detectors like ATLAS experiment and CMS experiment. The strange quark mass and its running with scale are central to studies by theorists such as Ken Wilson (renormalization), Gerard 't Hooft (gauge theories), and Steven Weinberg (electroweak theory). Its weak interactions are described by the Cabibbo–Kobayashi–Maskawa matrix developed by Nicola Cabibbo, Makoto Kobayashi, and Toshihide Maskawa, whose elements dictate flavor-changing transitions measured by collaborations including Belle experiment and BaBar experiment.

Role in Hadrons and Nuclear Physics

Strange quarks form part of mesons and baryons such as the Kaon (K meson), Lambda baryon, Sigma baryon, and Xi baryon, whose spectroscopy has been mapped by experiments at Jefferson Lab, CERN SPS, and J-PARC. Strange content influences properties of nuclear matter studied in contexts like neutron star modeling by researchers including Subrahmanyan Chandrasekhar and in heavy-ion collisions at Relativistic Heavy Ion Collider and LHC Heavy Ion programs. Phenomena such as kaon condensation, hypernuclei investigations at GSI Helmholtz Centre for Heavy Ion Research, and strangeness enhancement observed by the ALICE experiment provide links between microscopic quark content and macroscopic astrophysical and nuclear observables discussed by theorists like Edward Witten and David Gross.

Production and Detection

Strange quarks are produced in high-energy collisions via gluon splitting and quark pair production in processes studied at CERN LHC, Fermilab Tevatron (historically), and fixed-target facilities like CERN ISR and Protvino. Detection relies on reconstructing strange hadron decay topologies in detectors such as LHCb experiment, NA62 experiment, Hyper-Kamiokande (future neutrino-related studies), and bubble chamber experiments pioneered at CERN and Brookhaven National Laboratory. Signature techniques include displaced-vertex reconstruction, invariant mass analysis used by collaborations such as OPAL experiment and ALEPH experiment, and particle identification methods developed at KEK and DESY by groups including Takaaki Kajita's neutrino investigators and Arthur McDonald's collaborators on neutrino mass experiments.

History and Discovery

The history of strangeness began with cosmic-ray observations and cloud chamber photographs by experimentalists such as C. F. Powell and Donald Glaser, leading to anomalous long-lived particles called V-particles reported by teams at Brookhaven National Laboratory and CERN. Theoretical classification by Murray Gell-Mann and Kazuhiko Nishijima introduced the strangeness quantum number; the quark hypothesis by Murray Gell-Mann and George Zweig in 1964 incorporated the strange quark as an essential flavor. Further experimental confirmations came from deep inelastic scattering experiments at SLAC guided by Richard Feynman's parton model and from spectroscopic studies performed by collaborations at DESY and Fermilab, with contributions from theorists including James Bjorken and Sidney Drell.

Theoretical Framework and Quantum Numbers

In Quantum Chromodynamics, the strange quark transforms under the fundamental representation of SU(3) color and carries flavor SU(3) quantum numbers in the context of the Eightfold Way developed by Murray Gell-Mann and Yuval Ne'eman. Its flavor quantum number "strangeness" (S = −1 for an s quark) enters selection rules derived from symmetries studied in works by Noether (Noether's theorem) and Eugene Wigner (symmetry principles). CP-violation effects in kaon systems, investigated by teams at CERN and Fermilab and analyzed using the CKM matrix formalism, involve s↔d transitions with parameters constrained by experiments like NA48 experiment, KTeV experiment, LHCb experiment, and theoretical input from researchers including John Ellis and Hitoshi Murayama.

Category:Quarks