  Studying the acceleration and propagation mechanisms of Galactic cosmic rays
can provide information regarding astrophysical sources, the properties of our
Galaxy, and possible exotic sources such as dark matter. To understand cosmic
ray acceleration and propagation mechanisms, accurate measurements of different
cosmic ray elements over a wide energy range are needed. The PAMELA experiment
is a satellite-borne apparatus which allows different cosmic ray species to be
identified over background. Measurements of the cosmic ray antiproton flux and
the antiproton-to-proton flux ratio from 1.5 GeV to 180 GeV are presented in
this thesis. Compared to previous experiments, PAMELA extends the energy range
of antiproton measurements and provides significantly higher statistics. The
derived antiproton flux and antiproton-to-proton flux ratio are consistent with
previous measurements and generally considered to be produced as secondary
products when cosmic ray protons and helium nuclei interact with the
interstellar medium.
  To constrain cosmic ray acceleration and propagation models, the antiproton
data measured by PAMELA were further used together with the proton spectrum
reported by PAMELA, as well as the B/C data provided by other experiments.
Statistical tools were interfaced with the cosmic ray propagation package
GALPROP to perform the constraining analyses. Diffusion models with a linear
diffusion coefficient and modified diffusion models with a low energy
dependence of the diffusion coefficient were studied in the $\chi^{2}$ study.
Uncertainties on the parameters and the goodness of fit of each model were
given. Some models are further studied using the Bayesian inference. Posterior
means and errors of the parameters base on our prior knowledge on them were
obtained in the Bayesian framework. This method also allowed us to understand
the correlation between parameters and compare models.
