Measurement of the pd→pdη cross section in complete kinematics

The pd→pdη reaction has been studied in a kinematically complete experiment at five beam energies 927, 961, 996, 1032, and 1096 MeV. In contrast to our measurement of the pd→3Heη at the same energies, all the c.m. angular distributions are consistent with isotropy. The energy dependence of the total cross section seems to follow a three-body phase space as modified by a proton-deuteron final-state interaction, and such an extrapolation is consistent with other near-threshold data. The distributions of the pd and pη invariant mass at fixed beam energy are both close to those of phase space. However, this is not the case for the dη invariant mass, which shows significant structure in the first few MeV above threshold. This behavior is similar to that observed in the energy variation of the pn→dη total cross section and is the sign of a large η-deuteron scattering length that has been predicted in many theoretical models