Search for η mesic 3He with the WASA-at-COSY facility in the pd→3He2γ and pd →3He6γ reactions

Abstract

We report on the experimental search for the bound state of an ηmeson and 3Henucleus performed using the WASA-at-COSY detector setup. In order to search for the η-mesic nucleus decay, the pd→3He2γand pd →3He6γchannels have been analysed. These reactions manifest the direct decay of the ηmeson bound in a 3Henucleus.This non-mesonic decay channel has been considered for the first time. When taking into account only statistical errors, the obtained excitation functions reveal a slight indication for a possible bound state signal corresponding to a 3He-ηnucleus width above 20 MeV and binding energy Bsbetween 0 and 15 MeV. However, the determined cross sections are consistent with zero in the range of the systematic uncertainty. Therefore, as final result we estimate only the upper limit for the cross section of the η-mesic 3Henucleus formation followed by the ηmeson decay which varies between 2nb and 15nb depending on possible bound state parameters.