  In case of chiral U_A(1) symmetry restoration the mass of the eta' boson (the
ninth, would-be Goldstone boson) is decreased, thus its production cross
section is heavily enhanced. The eta' decays (through one of its decay
channels) into five pions. These pions will not be correlated in terms of
Bose-Einsten correlations, thus the production enhancement changes the strength
of two-pion correlation functions at low momentum. Preliminary results strongly
support the mass decrease of the eta' boson. In this paper we propose a method
to select pions coming from eta' decays. We investigate the efficiency of the
proposed kinematical cut in several collision systems and energies with several
simulators. We prove that our method can be used in all investigeted collision
systems.
