A search for rare and forbidden decays of η-meson with GAMS-4π

A search for the rare and forbidden neutral decays of η-meson with the GAMS-4π setup has been performed. The charge-exchange reaction at 32.5 GeV/c was used as a source of 3.7⋅106 η-mesons. At the 90% confidence level the following upper limits were obtained: BR(η→3γ)<1.6⋅10−4, BR(η→4γ)<2.8⋅10−4, BR(η→π°π°)<3.5⋅10−4, BR(η→π°π°γ)<1.7⋅10−3, BR(η→π°π°γγ)<4.0⋅10−3, BR(η→3π°γ)<2.4⋅10−4, BR(η→4π°)<2.0⋅10−5.