Quark

Quark
Name	Quark
Composition	Elementary particle
Statistics	Fermionic
Generation	First, second, third
Interactions	Strong, weak, electromagnetic, gravity
Theorized	Murray Gell-Mann (1964),, George Zweig (1964)
Discovered	SLAC (1968)
Mass	See properties
Electric charge	+2, 3e, −1, 3e
Color charge	Yes
Spin	1, 2

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 observable matter is composed of up quarks, down quarks, and electrons.

Overview

Quarks are the only elementary particles in the Standard Model of particle physics to experience all four fundamental interactions, also known as fundamental forces. They possess properties such as electric charge, color charge, mass, and spin, and are never found in isolation due to a phenomenon called color confinement. The theory describing the strong interaction between quarks is quantum chromodynamics, developed by physicists like David Gross, David Politzer, and Frank Wilczek. The discovery of quarks was a pivotal moment in the history of subatomic particle research.

Types and properties

There are six types, or flavors, of quarks: up, down, charm, strange, top, and bottom. Up and down quarks have the lowest masses and are the constituents of ordinary matter, found in protons and neutrons. Heavier flavors, such as charm and strange, are typically produced in high-energy collisions, like those at the Large Hadron Collider or the former Tevatron. Each quark flavor carries a fractional electric charge: +2/3 for up, charm, and top, and -1/3 for down, strange, and bottom. They also carry a type of charge called color charge, which is the source of the strong interaction.

History of quark theory

The quark model was independently proposed in 1964 by physicists Murray Gell-Mann and George Zweig. Gell-Mann coined the term "quark" from a line in James Joyce's novel Finnegans Wake. The model was developed to explain the patterns observed in the particle zoo of numerous hadrons discovered in the mid-20th century. Key theoretical developments included the concept of color charge and the formulation of quantum chromodynamics in the 1970s, which earned the Nobel Prize in Physics in 2004 for David Gross, David Politzer, and Frank Wilczek. The prediction of the charm quark by Sheldon Glashow, John Iliopoulos, and Luciano Maiani was another major milestone.

Experimental evidence

The first experimental evidence for quarks came in 1968 from deep inelastic scattering experiments conducted at the SLAC National Accelerator Laboratory by a team led by Jerome I. Friedman, Henry Way Kendall, and Richard E. Taylor, for which they received the Nobel Prize in Physics in 1990. These experiments probed the internal structure of the proton, revealing point-like constituents. The charm quark was discovered simultaneously in 1974 by teams at Brookhaven National Laboratory (led by Samuel Ting) and SLAC National Accelerator Laboratory (led by Burton Richter). The bottom quark was found at Fermilab in 1977, and the top quark was finally observed at Fermilab's Tevatron in 1995 after a long search.

Confinement and hadronization

Quarks are subject to color confinement, meaning they are never observed in isolation but are always bound within hadrons. This is a direct consequence of the nature of the strong interaction as described by quantum chromodynamics. When quarks are produced in high-energy collisions, such as those at the Large Hadron Collider, they undergo a process called hadronization, where they combine with other quarks or antiquarks to form a jet of hadrons, primarily mesons and baryons. The study of these jets is a key tool for physicists at laboratories like CERN and DESY.

Role in the Standard Model

Quarks are fundamental fermions in the Standard Model, which unifies the electroweak interaction and quantum chromodynamics. They interact via the exchange of gauge bosons: gluons mediate the strong force, while the W and Z bosons and the photon mediate the weak and electromagnetic forces, respectively. Quarks acquire mass through their interaction with the Higgs field, a mechanism confirmed by the discovery of the Higgs boson at CERN in 2012. The model's success in predicting phenomena like CP violation, studied at facilities like the KEK laboratory in Japan and the LHCb experiment, relies heavily on the properties and interactions of quarks.

Category:Quarks Category:Elementary particles Category:Standard Model