that energy and momentum conservation lead to a non-trivial dependence of the scaled variance on the location and magnitude of the observed fraction of momentum space. These predictions can be tested against existing and future data from the heavy ion collision experiments at the CERN SPS and BNL RHIC facilities.

The paper is organized as follows: In section \[model\] we briefly introduce our model. In section \[GCECE\] we consider multiplicity distributions in a limited region of momentum space in GCE and CE. For the MCE we follow, in section \[MCE\], the procedure of Ref.[@clt] and show how to calculate the width of the corresponding distributions in the large volume limit. We revisit the so-called ‘acceptance scaling‘ previously suggested as an approximate implementation of experimental acceptance in section \[Results\]. Technical details of the calculations are presented in the Appendix. Concluding remarks and a summary in sections \[Remarks\] and \[Summary\] close the paper.

The Model {#model}
=========

The ideal Boltzmann $\pi^+$ $\pi^-$ $\pi^0$ gas serves as the standard example throughout this paper, while the main subject of investigation is the multiplicity distribution $P(N_{\Omega})$ of particles with momenta inside a certain segment $\Omega$ of momentum space. Calculations are done for the three standard 