Abstrakt
Because of their small electromagnetic corrections, the isospin-breaking decays eta to 3 pi seem to be good candidates for extracting isospin-breaking parameters md-mu. This task is unfortunately complicated by large chiral corrections and the discrepancy between the experimentally measured values of the Dalitz parameters describing the energy dependence of the amplitudes of these decays and those predicted from chiral perturbation theory.
We present two methods based on an analytic dispersive representation that use the information from the NNLO chiral result and the one from the measurement of the charged eta to 3 pi decay by KLOE together in a harmonized way in order to determine the value of the quark mass ratio R. Our final result is R= 37.7 +/- 2.2.