  In nuclear collisions the incident protons generate a Coulomb field which
acts on produced charged particles. The impact of these interactions on charged
pion transverse-mass and rapidity spectra, as well as on pion-pion momentum
correlations is investigated in Au+Au collisions at $\sqrt{s_{NN}}$ = 2.4 GeV.
We show that the low-mt part of the data ($m_t < 0.2$ GeV/c$^2$) can be well
described with a Coulomb-modified Boltzmann distribution that also takes
changes of the Coulomb field during the expansion of the fireball into account.
The observed centrality dependence of the fitted mean Coulomb potential
deviates strongly from a $A_{part}^{2/3}$ scaling, indicating that, next to the
fireball, the non-interacting charged spectators have to be taken into account.
For the most central collisions, the Coulomb modifications of the HBT source
radii are found to be consistent with the potential extracted from the
single-pion transverse-mass distributions. This finding suggests that the
region of homogeneity obtained from two-pion correlations coincides with the
region in which the pions freeze-out. Using the inferred mean-square radius of
the charge distribution at freeze-out, we have deduced a baryon density, in
fair agreement with values obtained from statistical hadronization model fits
to the particle yields.
