  The transverse momentum spectra of hadrons is calculated from the
unintegrated gluon distribution (UGD) within the $k_T$-factorization framework
at small $x$. Starting from $pp$ collisions, the modification caused by the
nuclear medium is incorporated in the UGD at high energies, which is related to
the nuclear shadowing phenomenon. Moreover, we consider that particle
production from minijet decaying is not enough to explain the $p_T$ spectra in
$AA$ collisions due to collective phenomena that take place after the hard
collision. The Boltzmann-Gibbs Blast Wave (BGBW) distribution is utilized in
order to evaluate the distribution of particle production in equilibrium. Data
from ALICE collaboration for $PbPb$ collisions at $\sqrt{s}=2.76$ TeV are
analyzed and the nuclear modification factor for pion production is computed.
