Cross Section and Tensor Analysing Power of the $\vec{d}d\to ηα$ Reaction Near Threshold

Abstract

The angular distributions of the unpolarised differential cross section and tensor analysing power $A_{xx}$ of the $\vec{d}d\toαη$ reaction have been measured at an excess energy of 16.6 MeV. The ambiguities in the partial-wave description of these data are made explicit by using the invariant amplitude decomposition. This allows the magnitude of the s-wave amplitude to be extracted and compared with results published at lower energies. In this way, firmer bounds could be obtained on the scattering length of the $ηα$ system. The results do not, however, unambiguously prove the existence of a quasi-bound $ηα$ state.

20 pages, 11 figures