Upper limit on the η→γγγ branching ratio with the KLOE detector

=547.3 MeV.The KLOE detector consists of a large-volume drift chamber [3] (3.3 m lengthand 2 m radius), operated with a 90% helium-10% isobutane gas mixture, andasampling calorimeter [4]made oflead andscintillating fibres. The calorimeterconsists ofacylindrical barreland two endcaps providing a solid anglecoverageof 98%. A superconducting coil surrounds the entire detector and produces asolenoidal field B=0.52 T.Tracks are reconstructed in the drift chamber with a momentum resolution ofσ(p