  The aim of this Thesis is to contribute to the understanding of the nucleon
structure through the study of two observables accessible in Semi-Inclusive
Deep Inelastic Scattering (SIDIS) of high energy leptons off unpolarized
protons: the transverse-momentum distributions and the amplitudes of the
modulations in the azimuthal angle of the final state hadrons, the latter
referred to as "azimuthal asymmetries". They give relevant information on the
transverse momentum of the partons inside the nucleon and on the Boer-Mulders
TMD PDF. This Thesis summarizes the work done in this direction during my PhD,
which consisted in a complete analysis of part of the data collected in 2016 in
COMPASS, a fixed target experiment at the CERN SPS using 160 GeV/$c$ $\mu^+$
and $\mu^-$ beams and a liquid hydrogen target. The data quality and the
detector stability have been investigated, as well as the stability and the
consistency of the reconstructed data. A significant effort has been put in the
validation of the Monte Carlo simulations, necessary for the evaluation of the
acceptance of the spectrometer and to estimate the contamination to the SIDIS
sample by the hadrons produced in the decay of diffractively produced vector
mesons (particularly $\rho^0$ and $\phi$). This diffractive process had also to
be studied in detail and implemented in dedicated Monte Carlo simulations,
reducing the systematic uncertainties affecting previous measurements. Other
systematic effects have also been investigated, and the corresponding
systematic uncertainties evaluated. A deep inspection of the various kinematic
dependences has been performed. A phenomenological analysis of the new results
is also presented, with a comparison of the current COMPASS findings with the
previous ones obtained on a deuteron target.
