Measurement of the properties of the ${\eta }^{\mathcal{’}}$ and search for other resonances in γγ→η${\pi }^0$${\pi }^0$

The reaction $e^{+}$$e^{\mathrm{-}}$→$e^{+}$$e^{\mathrm{-}}$η${\pi }^0$${\pi }^0$ has been observed with the Crystal Ball detector at the DORIS II storage ring at DESY. The η${\pi }^0$${\pi }^0$ mass spectrum is dominated by the η’, and the two-photon width ${\Gamma }_{\eta \mathcal{’}\to \gamma \gamma }$ is determined to be 4.6±0.4±0.6 keV. Limits on ${\Gamma }_{X\to \gamma \gamma }$×$B_{X\to \eta \pi \pi }$ are given for other possible states.