Axial collective excitations of a degenerate Fermi gas in the BEC to   unitarity crossover
  We show that, with reasonable hypotheses leading to a simple modeling,a link can be obtained from experiments on the axial low frequency collective modes between the molecular scattering length $a_M$ and the energy parameter $\xi \equiv 1 + \beta$ of the gas at the unitarity limit. We also point out that, in order to reach the range where the features of the Bose limit can be clearly seen, experiments have to go to more dilute situations than have been achieved presently. 
R. Combescot and X. Leyronas