New intro
editThe quark (/kwɔrk/, /kwɑːk/ or /kwɑːrk/) is a type of subatomic particle which forms the most basic known building block of the atomic nucleus. It is distinguished from other matter particles because it interacts with the gluon through the strong force. As a result, stable quarks are always bound very tightly together in particles called hadrons; two of these, the proton and neutron, are themselves stable and account for almost all the mass of ordinary matter in the known universe.
There are six types of quarks: up, down, charm, strange, top, and bottom. Only the lightest, the up and down, are stable; the latter four are unstable and decay rapidly, and can be created and studied only under special conditions, such as in particle accelerators and in cosmic rays. Quark masses range from about half a percent of the proton mass for the up quark, up to more than the mass of a gold atom for the top quark.
In the early universe, the density of matter and energy was very high, and quarks appeared in very different forms than they are found in today. The heavier quarks existed in almost equal abundance to the light, stable ones. Physicists also believe that quarks did not form hadrons but were instead mixed together in a dense "soup" of quarks and gluons, called a quark-gluon plasma; as of 2008, experiments at ion colliders are still working to confirm and investigate this high-energy state of matter.
Physicists Murray Gell-Mann and George Zweig independently proposed the quark model in 1964 as a way of explaining the regular properties of hadrons, much in the same way that that the number of protons, neutrons, and electrons in atoms explains the regular properties of the periodic table of the chemical elements. The model initially only included the up, down, and strange quarks; the other three were proposed over the next few years in order to make the model self-consistent and allow it to predict a wider range of phenomena. The first direct evidence for the model was found in collisions between electrons and protons in 1968, which revealed that the proton is made of smaller particles, but the model was widely accepted only after the 1974 discovery of the charm quark. The bottom quark was first observed in 1977, and the top quark in 1995.
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A quark (/kwɔrk/, /kwɑːk/ or /kwɑːrk/) is one of two types of fermionic elementary particles in the Standard Model of particle physics, the other being the lepton.[1] The quark and the lepton are the two basic components of all matter.[2]
There are six different types of quarks, known as flavors: up, down, charm, strange, top, and bottom.[3] The charm, strange, top, and bottom flavors are unstable and decay rapidly, and can be created and studied only under special conditions, such as in particle accelerators and in cosmic rays. However, the up and down flavors are very common in the universe and are generally stable. For every quark flavor there is an antiparticle, called an antiquark, that differs from quarks only in that some of their properties are of opposite sign.
Due to a phenomenon known as color confinement, quarks do not exist as free particles in nature.[4] They are always bound together in composite particles named hadrons.[4] There are two types of hadrons: mesons (particles made of one quark and one antiquark) and baryons (particles made of three quarks).[5] Various combinations of the six flavors account for all of the known hadrons. Hadrons are differentiated by the specific quarks they contain and the manner in which they are combined.[3] The most famous and best known hadrons are protons and neutrons which make up the atomic nucleus. Since quarks are not found in isolation, their properties can only be deduced from experiments on hadrons.[4] (An exception to this rule is the top quark, which decays so rapidly that it does not produce hadrons at all, and instead observed through the identification of the particles it has decayed into.)
Physicists Murray Gell-Mann and George Zweig independently proposed the quark model in 1964.[6] There was little evidence for the theory until 1968, when electron-proton scatterings indicated the existence of small substructures within the proton.[7][8] By 1995, when the top quark was observed at Fermilab, all the six flavors had been observed and proven.
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edit- Actually, this is not my version. It's the revised version of my version. Some things were taken out that I wanted left in; compare to User:Ling.Nut/page3... I think SCZenz's version is an improvement over mine... though I'd still like to put some things back in...
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- Do we want to say anything about Quark-gluon plasma and the early universe?
A quark (/kwɔrk/, /kwɑːk/ or /kwɑːrk/) is one of two types of fermionic elementary particles in the Standard Model of particle physics, the other is the lepton.[9] The difference between quarks and leptons is that only quarks carry color charge, and hence, interact via the strong force.[10] Fermions interact via the third type of elementary particles called gauge bosons—one example of them is photon.
There are six different types of quarks, known as flavors. These flavors are up, down, charm, strange, top, and bottom.[3] The charm, strange, top, and bottom flavors are unstable, and can be created and studied only under special conditions. However, the up and down flavors are very common in the universe as the components of protons and neutrons. For every quark flavor there is also an antiparticle, called an antiquark, that differs from quarks only in that some of their properties are inverted.
Due to a phenomenon known as color confinement, quarks do not exist as free particles in nature.[11] They are always bound together as components of hadrons. There are two types of hadron: the mesons and baryons. Mesons consist of one quark and one antiquark, and baryons consist of three quarks.[12] Various combinations of the six flavors account for all of the known mesons and baryons; the hadrons are differentiated by the specific quarks they contain and the manner in which they are combined.[3] The best known hadrons are the protons and neutrons which make up the atomic nucleus. Since quarks are not directly observable,[11] their properties can only be deduced by experiments on hadrons.[13]
Physicists Murray Gell-Mann and George Zweig independently proposed the quark model in 1964.[6] There was little evidence for the theory until 1968, when the first up and down quarks were observed in an electron–proton scattering at the Stanford Linear Accelerator Center.[7][8] The remaining quark flavors were first observed between 1974 and 1995.
refs
edit- ^ "Fundamental Particles". Oxford Physics. Retrieved 2008-06-29.
- ^ "Quark (subatomic particle)". Encyclopedia Britannica. Retrieved 2008-06-29.
- ^ a b c d "Quarks". HyperPhysics. Retrieved 2008-06-29. Cite error: The named reference "Hyperphysics" was defined multiple times with different content (see the help page).
- ^ a b c Cite error: The named reference
Kimwas invoked but never defined (see the help page). - ^ "Theory: Hadrons (SLAC VVC)". Stanford Linear Accelerator Center. Retrieved 2008-08-18.
- ^ a b B. Carithers, P. Grannis. "Discovery of the Top Quark" (PDF). Retrieved 2008-09-23.
{{cite journal}}: Cite journal requires|journal=(help) - ^ a b E. D. Bloom (1969). "High-Energy Inelastic e-p Scattering at 6° and 10°". Physical Review Letters. 23: p.930. doi:10.1103/PhysRevLett.23.930.
{{cite journal}}:|pages=has extra text (help) Cite error: The named reference "Bloom" was defined multiple times with different content (see the help page). - ^ a b M. Breidenbach (1969). "Observed Behavior of Highly Inelastic Electron-Proton Scattering". Physical Review Letters. 23: p.935. doi:10.1103/PhysRevLett.23.935.
{{cite journal}}:|pages=has extra text (help) Cite error: The named reference "Breidenbach" was defined multiple times with different content (see the help page). - ^ "Fundamental Particles". Oxford Physics. Retrieved 2008-06-29.
- ^ "Quark (subatomic particle)". Encyclopedia Britannica. Retrieved 2008-06-29.
- ^ a b http://genesismission.jpl.nasa.gov/educate/scimodule/Cosmogony/CosmogonyPDF/FundamentalsST.pdf
- ^ "Theory: Hadrons (SLAC VVC)". Stanford Linear Accelerator Center. Retrieved 2008-08-18.
- ^ Kenway, Richard. (2002). Simulation of the strong interaction. Philosophical Transactions: Mathematical, Physical and Engineering Sciences, Vol. 360, No. 1795, New Science from High-Performance Computing, pp. 1123-1134. page 1124.