Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: 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.

10
The categories of this paper are: q-bio
1
The categories of this paper are: cs
3
The categories of this paper are: physics
19
The categories of this paper are: eess
27
The categories of this paper are: comp-gas
35
The categories of this paper are: mtrl-th
12
The categories of this paper are: nucl-th
11
The categories of this paper are: hep-lat
8
The categories of this paper are: hep-ex
37
The categories of this paper are: supr-con
18
The categories of this paper are: econ
23
The categories of this paper are: solv-int
34
The categories of this paper are: chem-ph
6
The categories of this paper are: astro-ph
21
The categories of this paper are: adap-org
0
The categories of this paper are: hep-ph