  We study the identified particle ratios produced at mid-rapidity in heavy ion
collisions, along with their correlations with the collision energy. We employ
our earlier proposed Unified Statistical Thermal Freeze-out Model (USTFM),
which incorporates the effects of both longitudinal as well as transverse
hydrodynamic flow in the hot hadronic system. A fair agreement seen between the
experimental data and our model results confirms that the particle production
in these collisions is of statistical nature. The variation of the chemical
freeze-out temperature and the baryon chemical potential with respect to
collision energies is studied. The chemical freeze-out temperature is found to
be almost constant beyond the RHIC energy and is found to be close to the QCD
predicted phase transition temperature suggesting that the chemical freeze-out
occurs soon after the hadronization takes place. The vanishing value of
chemical potential at LHC indicates very high degree of nuclear transparency in
the collision.
