Three-body final state interaction in $η\to 3 π$ updated

Abstract

In view of the recent high-statistic KLOE data for the η→π$^+$π$^−$π$^0$ decay, a new determination of the quark mass double ratio has been done. Our approach relies on a dispersive model that takes into account rescattering effects between three pions via subenergy unitarity. The latter is essential to reproduce the Dalitz plot distribution. A simultaneous description of the KLOE and WASA-at-COSY data is achieved in terms of just two real parameters. From a global fit, we determine Q=21.6±1.1. The predicted slope parameter for the neutral channel α=−0.025±0.004 is in reasonable agreement with the PDG average value.