  New sets of parameters ("tunes") for the underlying-event (UE) modeling of
the PYTHIA8, PYTHIA6 and HERWIG++ Monte Carlo event generators are constructed
using different parton distribution functions. Combined fits to CMS UE
proton-proton (pp) data at sqrt(s) = 7 TeV and to UE proton-antiproton (p
p-bar) data from the CDF experiment at lower sqrt(s), are used to study the UE
models and constrain their parameters, providing thereby improved predictions
for proton-proton collisions at 13 TeV. In addition, it is investigated whether
the values of the parameters obtained from fits to UE observables are
consistent with the values determined from fitting observables sensitive to
double-parton scattering processes. Finally, comparisons of the UE tunes to
"minimum bias" (MB) events, multijet, and Drell-Yan (q q-bar to Z / gamma* to
lepton-antilepton + jets) observables at 7 and 8 TeV are presented, as well as
predictions for MB and UE observables at 13 TeV.
