High-statistics measurement of the η→3π0 decay at the Mainz Microtron

Here, the largest, at the moment, statistics of 7 × 10 ⁶ η → 3π ⁰ decays, based on 6.2 × 10 ⁷ η mesons produced in the γp → ηp reaction, has been accumulated by the A2 Collaboration at the Mainz Microtron, MAMI. It allowed a detailed study of the η → 3π ⁰ dynamics beyond its conventional parametrization with just the quadratic slope parameter α and enabled, for the first time, a mea- surement of the second-order term and a better understanding of the cusp structure in the neutral decay. The present data are also compared to recent theoretical calculations that predict a nonlinear dependence along the quadratic distance from the Dalitz-plot center.