Measurement of the Slope Parameter $\alpha$ for the $\eta\to 3\pi^0$ decay with the Crystal Ball detector at the Mainz Microtron (MAMI-C)

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The dynamics of the $\eta\to 3\pi^0$ decay have been studied with the Crystal Ball multiphoton spectrometer and the TAPS calorimeter.

• Bremsstrahlung photons produced by the 1.5-GeV electron beam of the Mainz microtron MAMI-C and tagged by the Glasgow photon spectrometer were used for $\eta$-meson production.
• The analysis of $3 \times 10^6$ $\gamma p \to \eta p \to 3\pi^0 p \to 6\gamma p$ events yields the value $\alpha=-0.032\pm0.003$ for the $\eta\to 3\pi^0$ slope parameter, which agrees with the majority of recent experimental results and has the smallest uncertainty.
• The $\pi^0\pi^0$ invariant-mass spectrum was investigated for the occurrence of a cusplike structure in the vicinity of the $\pi^+\pi^-$ threshold.