Search for the η-mesic Helium bound state with the WASA-at-COSY facility

We performed a search for ⁴He-η bound state with high statistics and high acceptance with the WASA-at-COSY facility using a ramped beam technique. The signature of η-mesic nuclei is searched for in dd → ³Henπ⁰ and dd → ³Hepπ^- reactions by the measurement of the excitation functions in the vicinity of the η production threshold. This paper presents the experimental method and the preliminary results of the data analysis for dd → ³Henπ⁰ process.The obtained excitation function does not show any narrow structure which could be a signature of the bound state with width less than 50 MeV. The upper limit is by a factor of 5 larger than theoretically predicted value therefore, the current measurement does not exclude the existence of bound state in this process