Eta puzzle: the decay eta. --> pi. /sup 0/. gamma gamma

Experiments have been carried out to search for the decay eta..--> pi../sup 0/..gamma gamma.. 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 ..gamma.. spectrometer GAMS-2000. It is shown that the decay eta..--> pi../sup 0/..gamma gamma.. 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..--> pi../sup 0/..gamma gamma..)<3 x 10/sup -3/.