2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/177407A new high precision measurement of the $J/ψ$- and $ψ'$-meson masses has been performed at the VEPP-4M collider using the KEDR detector. The resonant depolarization method has been employed for the absolute calibration of the beam energy. The following mass values have been obtained: $M_{J/ψ} = 3096.917 \pm 0.010 \pm 0.007$ MeV, $M_{ψ'} = 3686.111 \pm 0.025 \pm 0.009$ MeV. The relative measurement accuracy has reached $4. 10^{-6}$ for $J/ψ$ and $7. 10^{-6}$ for $ψ'$, approximately 3 times better than in the previous precise experiments.12 pages, 4 tables, 10 figuresHigh Energy Physics - Experimenttext