Measurement of the $\eta^\prime$ and Search for Other Resonances in $\gamma \gamma \to \eta \pi^0 \pi^0$
Antreasyan, D., Bartels, H. W. S., Besset, D., Bieler, C., Bienlein, J. K., Bizzeti, A., Bloom, Elliott D., Brock, I., Brockmuller, K., Cabenda, R., Cartacci, A., Cavalli-Sforza, M., Clare, R., Conforto, G., Cooper, S., Cowan, R., Coyne, D. G., Drews, G., Edwards, C., Engler, A. · OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information) · 1987
The reaction e+e−→e+e−ηπ0π0 has been observed with the Crystal Ball detector at the DORIS II storage ring at DESY. The ηπ0π0 mass spectrum is dominated by the η’, and the two-photon width Γη’→γγ is determined to be 4.6±0.4±0.6 keV. Limits on ΓX→γγ×BX→ηππ are given for other possible states.