  Identical particle correlations at fixed multiplicity are considered by means
of quantum canonical ensemble of finite systems. We calculate one-particle
momentum spectra and two-particle Bose-Einstein correlation functions in the
ideal gas by using a recurrence relation for the partition function. Within
such a model we investigate the validity of the thermal Wick's theorem and its
applicability for decomposition of the two-particle distribution function. The
dependence of the Bose-Einstein correlation parameters on the average momentum
of the particle pair is also investigated. Specifically, we present the
analytical formulas that allow one to estimate the effect of suppressing the
correlation functions in a finite canonical system. The results can be used for
the femtoscopy analysis of the A+A and p+p collisions with selected (fixed)
multiplicity.
