Study of transverse-momentum--dependent parton distribution functions.
Rossi L., Bacchetta A.
The dynamics and the interactions between quarks and gluons are governed by the theory of Quantum chromodynamics (QCD), which exhibits asymptotic freedom. Two examples of high-energy processes are the Semi-Inclusive Deep Inelastic Scattering (SIDIS) and the Drell-Yan process. These are very interesting because, thanks to different factorization theorems, we can write their cross-sections in a factorized way by using the Transverse-Momentum--Dependent Parton Distribution Functions (TMD-PDFs) and Fragmentation Functions (TMD-FFs). These functions are crucial in understanding the three-dimensional structure of hadrons, because they give us information about their internal structure. For example, the TMD-PDFs give us the joint probability density of finding a particle with a certain fraction $x$ of nucleon momentum and transverse momentum $k_T$ inside the hadron. Moreover, these functions can be written as a product of a perturbative part, which has already been calculated at different orders, times a non-perturbative part, which can be extracted from the experimental data. We will present some results obtained from the extractions we have done regarding it.