  Suppression of high $p_T$ hadron spectra in high-energy heavy-ion collisions
at different energies is studied within a pQCD parton model incorporating
medium induced parton energy loss. The $p_T$ dependence of the nuclear
modification factor $R_{AA}(p_T)$ is found to depend on both the energy
dependence of the parton energy loss and the power-law behavior of the initial
jet spectra. The high $p_T$ hadron suppression at $\sqrt{s}=62.4$ GeV and its
centrality dependence are studied in detail. The overall values of the
modification factor are found to provide strong constraints on the lifetime of
the dense matter.
