  We provide the power spectrum of small scalar perturbations propagating in an
inflationary scenario within loop quantum cosmology. We consider the hybrid
quantization approach applied to a Friedmann--Robertson--Walker spacetime with
flat spatial sections coupled to a massive scalar field. We study the quantum
dynamics of scalar perturbations on an effective background within this hybrid
approach. We consider in our study adiabatic states of different orders. For
them, we find that the hybrid quantization is in good agreement with the
predictions of the dressed metric approach. We also propose an initial vacuum
state for the perturbations, and compute the primordial and the anisotropy
power spectrum in order to qualitatively compare with the current observations
of Planck mission. We find that our vacuum state is in good agreement with
them, showing a suppression of the power spectrum for large scale anisotropies.
We compare with other choices already studied in the literature.
