  Two-boson momentum correlations at fixed particle number constraint are
studied in a simple analytically solvable model of a thermal expanding system.
We show that the increase of expansion rate, as well as increase of particle
multiplicity, enhances the ground-state contribution to particle momentum
spectra and leads to suppression of the Bose-Einstein momentum correlations.
The relations of these findings to the multiplicity-dependent measurements of
the Bose-Einstein momentum correlations in high-multiplicity $p+p$ collision
events at the LHC are discussed.
