2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/179026The hadronic decays of the tau lepton can be used to determine the effective charge alpha_tau(m^2_tau') for a hypothetical tau-lepton with mass in the range 0 < m_tau' < m_tau. This definition provides a fundamental definition of the QCD coupling at low mass scales. We study the behavior of alpha_tau at low mass scales directly from first principles and without any renormalization-scheme dependence by looking at the experimental data from the OPAL Collaboration. The results are consistent with the freezing of the physical coupling at mass scales s = m^2_tau' of order 1 GeV^2 with a magnitude alpha_tau ~ 0.9 +/- 0.1.15 pages, 4 figures, submitted to Physical Review D, added references, some text added, no results nor figures changedHigh Energy Physics - PhenomenologyHigh Energy Physics - ExperimentHigh Energy Physics - Theorytext