Measurement of the Quasifree $\mathit{p}+\mathit{n}\to \mathit{d}+\mathit{\eta }$ Reaction near Threshold

The quasifree $p+n\to d+\eta$ reaction cross section has been measured in the near-threshold region using deuterium from an internal cluster-jet target and 1350 MeV protons in the CELSIUS storage ring of the The Svedberg Laboratory, Uppsala. The energy dependence of the cross section is extracted by exploiting the Fermi momentum of the target neutron and reconstructing the kinematics on an event-by-event basis. The data cover center of mass excess energies from 16 to 113 MeV.