Introduction

The basic assumption is that there is a monotonic relation between the centrality and the charged particle multiplicity $M$ of the collisions.

We can obtain a measure for the number of charged particles in the acceptance of the tiles from the energy deposited in them. It should be emphasized that what we label $M$ is strictly speaking, not the charged particle multiplicity; how it is calculated is described in detail in appendix C. By cutting in $M$ we can thus select event centrality.