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Hence, the actual value of the coupling constant is only defined at a given energy scale. In QCD, the Z boson mass scale is typically chosen, providing a value of the strong coupling constant of α s (M Z 2) = 0.1179 ± 0.0010. [7] In 2023 Atlas measured α s (M Z 2) = 0.1183 ± 0.0009 the most precise so far.
In particle physics, Yukawa's interaction or Yukawa coupling, named after Hideki Yukawa, is an interaction between particles according to the Yukawa potential. Specifically, it is between a scalar field (or pseudoscalar field) ϕ {\displaystyle \ \phi \ } and a Dirac field ψ {\displaystyle \ \psi \ } of the type
The strong force is the expression of the gluon interaction with other quark and gluon particles. All quarks and gluons in QCD interact with each other through the strong force. The strength of interaction is parameterized by the strong coupling constant.
The value of the fine-structure constant α is linked to the observed value of this coupling associated with the energy scale of the electron mass: the electron's mass gives a lower bound for this energy scale, because it (and the positron) is the lightest charged object whose quantum loops can contribute to the running.
For quantum chromodynamics, the constant changes with respect to the distance between the particles. This phenomenon is known as asymptotic freedom. Forces which have a coupling constant greater than 1 are said to be "strongly coupled" while those with constants less than 1 are said to be "weakly coupled." [7]
The strong coupling constant is conventionally labelled g s (or simply g where there is no ambiguity). The observations leading to the discovery of this part of the Standard Model are discussed in the article in quantum chromodynamics .
The weak interaction has a coupling constant (an indicator of how frequently interactions occur) between 10 −7 and 10 −6, compared to the electromagnetic coupling constant of about 10 −2 and the strong interaction coupling constant of about 1; [13] consequently the weak interaction is "weak" in terms of intensity. [14]
The confinement scale or QCD scale is the scale at which the perturbatively defined strong coupling constant diverges. This is known as the Landau pole.The confinement scale definition and value therefore depend on the renormalization scheme used.