Quark.docx

1、QuarkQuarkFrom Wikipedia, the free encyclopediaJump to: navigation, search This article is about the particle. For other uses, see Quark (disambiguation).QuarkA proton, composed of two up quarks and one down quark. (The color assignment of individual quarks is not important, only that all three colo

2、rs are present.)CompositionElementary particleStatisticsFermionicGeneration1st, 2nd, 3rdInteractionsElectromagnetism, Gravitation, Strong, WeakSymbolqAntiparticleAntiquark (q)TheorizedMurray Gell-Mann (1964)George Zweig (1964)DiscoveredSLAC (1968)Types6 (up, down, strange, charm, bottom, and top)Ele

3、ctric charge+23e, 13eColor chargeYesSpin12Baryon number13A quark (/kwrk/ or /kwrk/) is an 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.1 Due t

4、o a phenomenon known as color confinement, quarks are never directly observed or found in isolation; they can only be found within baryons or mesons.23 For this reason, much of what is known about quarks has been drawn from observations of the hadrons themselves.There are six types of quarks, known

5、as flavors: up, down, strange, charm, bottom, and top.4 Up and down quarks have the lowest masses of all quarks. The heavier quarks rapidly change into up and down quarks through a process of particle decay: the transformation from a higher mass state to a lower mass state. Because of this, up and d

6、own quarks are generally stable and the most common in the universe, whereas strange, charm, top, and bottom quarks can only be produced in high energy collisions (such as those involving cosmic rays and in particle accelerators).Quarks have various intrinsic properties, including electric charge, c

7、olor charge, spin, and mass. Quarks are the only elementary particles in the Standard Model of particle physics to experience all four fundamental interactions, also known as fundamental forces (electromagnetism, gravitation, strong interaction, and weak interaction), as well as the only known parti

8、cles whose electric charges are not integer multiples of the elementary charge. For every quark flavor there is a corresponding type of antiparticle, known as antiquark, that differs from the quark only in that some of its properties have equal magnitude but opposite sign.The quark model was indepen

9、dently proposed by physicists Murray Gell-Mann and George Zweig in 1964.5 Quarks were introduced as parts of an ordering scheme for hadrons, and there was little evidence for their physical existence until deep inelastic scattering experiments at the Stanford Linear Accelerator Center in 1968.67 All

10、 six flavors of quark have since been observed in accelerator experiments; the top quark, first observed at Fermilab in 1995, was the last to be discovered.5Contentshide 1 Classification 2 History 3 Etymology 4 Properties o 4.1 Electric chargeo 4.2 Spino 4.3 Weak interactiono 4.4 Strong interaction

11、and color chargeo 4.5 Masso 4.6 Table of properties 5 Interacting quarks o 5.1 Sea quarkso 5.2 Other phases of quark matter 6 See also 7 Notes 8 References 9 Further reading 10 External linksedit ClassificationSee also: Standard ModelSix of the particles in the Standard Model are quarks (shown in pu

12、rple). Each of the first three columns forms a generation of matter.The Standard Model is the theoretical framework describing all the currently known elementary particles, as well as the unobservednb 1 Higgs boson.8 This model contains six flavors of quarks (q), named up (u), down (d), strange (s),

13、 charm (c), bottom (b), and top (t).4 Antiparticles of quarks are called antiquarks, and are denoted by a bar over the symbol for the corresponding quark, such as u for an up antiquark. As with antimatter in general, antiquarks have the same mass, mean lifetime, and spin as their respective quarks,

14、but the electric charge and other charges have the opposite sign.9Quarks are spin-12 particles, implying that they are fermions according to the spin-statistics theorem. They are subject to the Pauli exclusion principle, which states that no two identical fermions can simultaneously occupy the same

15、quantum state. This is in contrast to bosons (particles with integer spin), any number of which can be in the same state.10 Unlike leptons, quarks possess color charge, which causes them to engage in the strong interaction. The resulting attraction between different quarks causes the formation of co

16、mposite particles known as hadrons (see Strong interaction and color charge below).The quarks which determine the quantum numbers of hadrons are called valence quarks; apart from these, any hadron may contain an indefinite number of virtual (or sea) quarks, antiquarks, and gluons which do not influence