  $Z^0$-boson production at low transverse momentum offers an unique
opportunity to explore the non-perturbative Sudakov factor. In this paper, we
employ three parameterizations of the non-perturbative Sudakov factor to
calculate the $\phi^*$-distribution and compare our results with the ultra
precise experimental data. We extract the free parameters in each
parameterization with a $\chi^2$ analysis. The parton-momentum-fraction
dependence of these free parameters is also studied by comparing the values
extracted at different collision energies and different rapidity ranges.
