  The number of particles detected in a nucleus-nucleus collision strongly
depends on the impact parameter of the collision. Therefore, multiplicity
fluctuations, as well as rapidity correlations of multiplicities, are dominated
by impact parameter fluctuations. We present a method based on Bayesian
inference which allows for a robust reconstruction of fluctuations and
correlations at fixed impact parameter. We apply the method to ATLAS data on
the distribution of charged multiplicity and transverse energy. We argue that
multiplicity fluctuations are smaller at large rapidity than around central
rapidity. We suggest simple, new analyses, in order to confirm this effect.
