= Heavy quark
A heavy quark has a <mass> large compared with the characteristic low-energy scale of <quantum chromodynamics>. <Charm quarks>, <bottom quarks> and <top quarks> are usually called heavy; treating charm as asymptotically heavy is a less accurate approximation than the corresponding treatment of bottom.
The separation of scales permits an expansion in inverse quark mass for many properties of a <hadron> containing one heavy quark. In the leading limit, the light degrees of freedom respond chiefly to the heavy quark's color field, with reduced sensitivity to its <spin> and precise flavor. This helps relate patterns in heavy-hadron <spectroscopy> and decays. The <top quark> is a special case: it decays before forming ordinary long-lived hadrons, so not every bound-state argument for charm and bottom applies to it.
Back to article page
