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In QCD electron-positron annihilation there is often the talk of hard processes and I am not a 100% sure about the definition of this term.

Does hard processes simply refer to all processes in the region of a small coupling constant $\alpha_s$?

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Hard processes are those in which the momentum transfer, $Q$, is substantial with respect to the QCD scale, $$Q > \Lambda_\text{QCD}\simeq 220 \,\text {MeV} .$$ In this regime, the strong coupling constant $\alpha_S$ is perturbative. In contrast, non-perturbative effects in soft emission requires complicated techniques (e.g. showering).

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  • $\begingroup$ ΛQCD is approximately 330 MeV. $\endgroup$ – ohwilleke Oct 18 '16 at 10:23

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