Eta puzzle: the decay eta→π0γγ

Experiments have been carried out to search for the decay eta→π0γγ at a level of accuracy ten times better than that in earlier studies in which this decay was observed. The measurements were carried out at the 70 GeV IHEP accelerator using the hodoscopic γ spectrometer GAMS-2000. It is shown that the decay eta→π0γγ was not observed in the earlier studies. An upper limit is obtained for the partial width of this decay at the 90% confidence level: BR (eta→π0γγ)<3 x 10-3