Direct observation of three-neutron emission from He * 7 and the search for the trineutron

This is the authors' abstract. We don't add key points for this paper.

Three-neutron emission from He 7 has been directly measured for the first time, following neutron knockout from a He 8 beam at 156 MeV/nucleon. A resonancelike structure at 2.08(4) MeV above the He 4 + 3 n threshold [ E x = 2.68 ( 4 ) MeV] with a width of 3.9(2) MeV was observed and deduced to arise predominately from the predicted J π = 3 / 2 2 − level. The three-neutron invariant-mass spectrum was reconstructed and found to peak at around 1 MeV and could, through complete simulations incorporating neutron-neutron correlations, be very well described by the sequential decay of He * 7 via the 2 1 + excited state of He 6 . No evidence was found for any significant three-neutron correlations beyond those expected from well-established two-body interactions, including a trineutron resonance.