up quark
Noun
Meaning
up quark (plural up quarks)
(physics) A quark having a fractional electric charge of
+
2
3
{\displaystyle +{\frac {2}{3}}}
and a mass of about 1.5 to 4 MeV.Symbol:
u
{\displaystyle u}
Hypernyms
Examples
A neutron composed of two down quarks and an up quark, decays to a proton composed of a down quark and two up quarks, for example.
At the quark level, W − emission turns a down quark into an up quark, turning a neutron (one up quark and two down quarks) into a proton (two up quarks and one down quark).
For example, an up quark with a spin of + 1 2 along the z axis is denoted by u↑.
Neutrons consist of one up quark and two down quarks.
The similarity in mass can be explained roughly by the slight difference in mass of up quark and down quark composing the nucleons.