The constraining method should remove any systematic effect due to the energy calibration of the electromagnetic calorimeter. However, a systematic effect can survive if the geometry of the calorimeter is incorrect.
To explore any possible remaining systematic, we reconstruct the decays and where the mesons decay via the golden modes , , and . We then compare the measured mass differences with the PDG  values. The results of this study are shown in sc_mass:dpi0_mass. We see that our measurements of the masses are accurate to within 0.1 . Taking into account the larger phase space available in , we estimate our systematic error on to be 0.3 or less.