Search for the forbidden decays η→3γ and η→π0γ and the rare decay η→π0π0γγ

A new upper limit is presented for the branching ratio (BR) of eta -> 3 gamma. This decay is not allowed by charge-conjugation invariance. We have determined that BR(eta -> 3 gamma)< 4x10(-5). We also obtained BR(eta ->pi(0)gamma -> 3 gamma)< 9x10(-5); this decay mode is absolutely forbidden, as it violates conservation of angular momentum. Finally, we have established that BR(eta ->pi(0)pi(0)gamma gamma)< 1.2x10(-3) in a restricted diphoton-energy region. All three upper limits are at the 90% confidence level. They were obtained by using the Crystal Ball multiphoton spectrometer at the AGS and are based on the analysis of 28 million eta mesons produced in the pi(-)p ->eta n reaction close to threshold.