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

TL;DR

This study measures angular distributions and tensor analysing power in the $oldsymbol{d}d ooldsymbol{ extalpha}oldsymbol{ exteta}$ reaction near threshold to better understand the $oldsymbol{ exteta}oldsymbol{ extalpha}$ interaction and scattering length.

Contribution

It provides new measurements of angular distributions and tensor analysing power at 16.6 MeV, and uses invariant amplitude decomposition to refine bounds on the $ exteta extalpha$ scattering length.

Findings

Extracted the magnitude of the s-wave amplitude.

Compared results with lower energy data.

Did not confirm the existence of a quasi-bound $ exteta extalpha$ state.

Abstract

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.