Cross Section and Tensor Analysing Power of the $\vec{d}d\to \eta\alpha$   Reaction Near Threshold
  The angular distributions of the unpolarised differential cross section and tensor analysing power $A_{xx}$ of the $\vec{d}d\to\alpha \eta$ 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 $\eta \alpha$ system. The results do not, however, unambiguously prove the existence of a quasi-bound $\eta \alpha$ state. 
The GEM Collaboration: A. Budzanowski, A. Chatterjee, R. Gebel, P.   Hawranek, R. Jahn, V. Jha, K. Kilian, S. Kliczewski, Da...