- Up quark
name = Up Quark
generation = First
mass = 1.5 - 3.3
electric_charge = +2/3 e
spin = ½
The up quark is a particle described by the
Standard Modeltheory of physics. It is a first-generation quarkwith a charge of +(2/3)"e". It is the lightest of all quarks. Its bare massis not well determined, but probably lies between 1.5 and 4 MeV. According to the Standard Modelof particle physics, there are six quark types. Ordinary matter, such as atoms, contains electrons and a nucleus. The protonsand neutronsinside the nucleus are called nucleons, and the up quark—along with the down quark-is the fundamental constituents of these nucleons. The proton contains two up quarks and a down quark, while the neutron contains one up quark and two down quarks.
The equivalence of mass and energy described in the theory of
Special Relativitymeans that quickly moving particles have greater energy and so appear to have a greater mass at high speeds than while at rest. [ [http://www2.slac.stanford.edu/vvc/theory/relativity.html Theory: Special Relativity (SLAC VVC) ] ] The strength of the strong forces holding the quarks in the nucleus suggests they are moving with relativistic speeds. Therefore, the majority of the mass in nucleons comes from the energy in the gluon field holding the quarks together, and not the quark masses themselves. The existence of up quarks was first postulated when Gell-Mannand Zweig developed the quark modelin 1964, and the first evidence for them was found in deep inelastic scatteringexperiments at SLACin 1967.
Hadrons containing up quarks
Some of the
hadronscontaining up quarks include:
Pions (SubatomicParticle|Pion+-) are mesons containing an up quark and an anti- down quark, or vice versa. [cite book|title=The Quantum World: Quantum Physics for Everyone|last=Ford|first=Kenneth William|pages=72|isbn=067401832X|publisher=Harvard University Press|year=2004]
*The neutral pion (SubatomicParticle|Pion0) is a
linear combinationof up-antiup and down-antidown, as are the ρ and ω mesons. [cite web|url=http://hyperphysics.phy-astr.gsu.edu/Hbase/particles/hadron.html|title=Mesons - pion|accessdate=6 July|accessyear=2008]
*The SubatomicParticle|Eta and SubatomicParticle|Eta prime flavorless mesons are
linear combinations of several quark-antiquark pairs, including up-antiup.
*A large number of detected
baryons contain one or more up quarks. Like the nucleons, the SubatomicParticle|Delta baryons are made of only up and down quarks: the SubatomicParticle|Delta++ contains three up quarks, the SubatomicParticle|Delta+ contains two, the SubatomicParticle|Delta0 contains only one while the SubatomicParticle|Delta-contains none.
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