This thesis discusses in detail the measurement of the polarizations of all S-wave vector
quarkonium states in LHC proton-proton collisions with the CMS detector. Heavy quarkonium
states constitute an ideal laboratory to study non-perturbative effects of quantum
chromodynamics and to understand how quarks bind into hadrons.The experimental results are
interpreted through an original phenomenological approach which leads to a coherent picture of
quarkonium production cross sections and polarizations within a simple model dominated by one
single color-octet production mechanism. These findings provide new insights into the dynamics
of heavy quarkonium production at the LHC an important step towards a satisfactory
understanding of hadron formation within the standard model of particle physics.
