Up quark


Up quark

Infobox Particle
bgcolour =
name = Up Quark


caption =
num_types =
composition = Elementary particle
family = Fermion
group = Quark
generation = First
interaction =
particle =
antiparticle =
theorized =
discovered =
symbol =
mass = 1.5 - 3.3 MeV/c2
decay_time =
decay_particle =
electric_charge = +2/3 e
color_charge =
spin = ½
num_spin_states =

The up quark is a particle described by the Standard Model theory of physics. It is a first-generation quark with a charge of +(2/3)"e". It is the lightest of all quarks. Its bare mass is not well determined, but probably lies between 1.5 and 4 MeV. According to the Standard Model of particle physics, there are six quark types. Ordinary matter, such as atoms, contains electrons and a nucleus. The protons and neutrons inside 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 Relativity means 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-Mann and Zweig developed the quark model in 1964, and the first evidence for them was found in deep inelastic scattering experiments at SLAC in 1967.

Hadrons containing up quarks

Some of the hadrons containing up quarks include:
*Positively Charged 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 combination of 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.

See also

*Isospin

References


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