  We demonstrate the occurrence of free quasi-particle excitations obeying
generalised exclusion statistics in a BCS model with asymmetric pair
scattering. The results are derived from an exact solution of the Hamiltonian,
which was obtained via the algebraic Bethe ansatz utilising the representation
theory of an underlying Yangian algebra. The free quasi-particle excitations
are associated to highest-weight states of the Yangian algebra, corresponding
to a class of analytic solutions of the Bethe ansatz equations.
