Running coupling constant and correlation length from Wilson loops

We consider a definition of the QCD running coupling constant $\alpha (\mu )$ related to Wilson loops of size $r\times t$ with arbitrary fixed $t\mathrm{/}r$. The schemes defined by these couplings are very close to the $\overline{\mathrm{M}\mathrm{S}}$ scheme for all values of $t\mathrm{/}r$; in the $t\mathrm{/}r\to \mathrm{\infty }$ limit, the ``$q\bar{q}$ force’’ scheme is recovered. We propose a definition of correlation length, also related to Wilson loops, which can be applied to the Monte Carlo evaluation of $\alpha (\mu )$ up to very large momentum scales by use of finite-size scaling techniques.