  The origin of the apparent thermalization in high-energy collisions is
investigated using the data of the ATLAS and CMS Collaborations at the LHC. For
this purpose, we analyze the transverse momentum distributions in the following
proton-proton collision processes, all at $\sqrt{s} = 13$ TeV: i) inclusive
inelastic $pp$ collisions; ii) single- and double-diffractive Drell-Yan
production $pp \to \mu^+ \mu^- X$; and iii) Higgs boson production. We confirm
the relation between the effective temperature and the hard scattering scale
observed at lower energies, and find that it extends even to the Higgs boson
production process. In addition we find that the thermal component disappears
in diffractive events (even though many charged hadrons are still produced). We
discuss the implications of our study for the mechanism of multi-particle
production -- in particular, we test the hypothesis about the link between
quantum entanglement and thermalization in high-energy collisions.
