  Experimental measurements of Drell-Yan (DY) vector-boson production are
available from the Large Hadron Collider (LHC) and from lower-energy collider
and fixed-target experiments. In the region of low vector-boson transverse
momenta $q_T$, which is important for the extraction of the $W$-boson mass at
the LHC, QCD contributions from non-perturbative Sudakov form factors and
intrinsic transverse momentum distributions become relevant. We study the
potential for determining such contributions from fits to LHC and lower-energy
experimental data, using the framework of low-$q_T$ factorization for DY
differential cross sections in terms of transverse momentum dependent (TMD)
distribution functions. We investigate correlations between different sources
of TMD non-perturbative effects, and correlations with collinear parton
distributions. We stress the relevance of accurate DY measurements at low
masses and with fine binning in transverse momentum for improved determinations
of long-distance contributions to Sudakov evolution processes and TMDs.
