  We propose a new revised Landau hydrodynamic model to study systematically
the pseudorapidity distributions of charged particles produced in heavy ion
collisions over an energy range from a few GeV to a few TeV per nucleon pair.
The interacting system is divided into three sources namely the central,
target, and projectile sources respectively. The large central source is
described by the Landau hydrodynamic model and further revised by the
contributions of the small target/projectile sources. In the calculation, to
avoid the errors caused by an unapt conversion or non-division, the rapidity
and pseudorapidity distributions are obtained respectively. The modeling
results are in agreement with the available experimental data at relativistic
heavy ion collider (RHIC), large hadron collider (LHC), and other energies for
different centralities. The value of square speed of sound parameter in
different collisions has been extracted by us from the widths of rapidity
distributions. Our results show that, in heavy ion collisions at RHIC and LHC
energies, the central source undergoes through a phase transition from hadronic
gas to quark-gluon plasma (QGP) liquid phase; meanwhile, the target/projectile
sources remain in the state of hadronic gas. The present work confirms that the
QGP is of liquid type rather than that of a gas. The whole region of
participants undergoes through a mixed phase consisting of a large quantity of
(>90%) QGP liquid and a small quantity of (<10%) hadronic gas.
