  Assuming that the final state of hadronization takes place along the
freezeout line, which is defined by a constant entropy density, the
antiproton-to-proton ratios produced in heavy-ion collisions are studied in
framework of the hadron resonance gas (HRG) model. A phase transition from
quark--gluon plasma to hadrons, a hadronization, has been conjectured in order
to allow modifications in the phase space volume and thus in single--particle
distribution function. Implementing both modifications in the grand--canonical
partition function and taking into account the experimental acceptance in
heavy-ion collisions, the antiproton-to-proton ratios over center-of-mass
energies $\sqrt{s}$ ranging from AGS to RHIC are very well reproduced by the
HRG model. Comparing with the same particle ratios in $pp$ collisions results
in a gradually narrowing discrepancy with increasing $\sqrt{s}$. At LHC energy,
the ALICE antiproton-to-proton ratios in $pp$ collisions turn to be very well
described by HRG model as well. It is likely that the ALICE heavy-ion program
will produce the same antiproton-to-proton ratios as the $pp$ program.
Furthermore, the ratio gets very close to unity indicating that the
matter-antimatter asymmetry nearly vanishes. The chemical potential calculated
at this energy strengthens the assumption of almost fully matter-antimatter
symmetry at LHC energy.
