2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/177789High statistics Dalitz-plot distribution of $η\to π^+π^-π^0$ decay obtained recently by KLOE collaboration \cite{kloe} is fitted to the results of corresponding theoretical calculations in Chiral Perturbation Theory (ChPT) with unitarity corrections taken into account. The quark mass ratio $Q = \sqrt{(m^2_s - (m_d + m_u)^2/4)/(m^2_d - m^2_u)} $ can be otained from this analysis. We get $Q= 22.8\pm 0.4$ which differs from the value $Q_{DT} = 24.2$ that follows from Dashen's theorem and agrees with recently calculated electromagnetic kaon mass difference.2 pages, no figuresHigh Energy Physics - Phenomenologytext