  We study the fermion pair production from a strong electric field in
boost-invariant coordinates in (3+1) dimensions and exploit the cylindrical
symmetry of the problem. This problem has been used previously as a toy model
for populating the central-rapidity region of a heavy-ion collision (when we
can replace the electric by a chromoelectric field). We derive and solve the
renormalized equations for the dynamics of the mean electric field and current
of the produced particles, when the field is taken to be a function only of the
fluid proper time $\tau = \sqrt{t^2-z^2}$. We determine the proper-time
evolution of the comoving energy density and pressure of the ensuing plasma and
the time evolution of suitable interpolating number operators. We find that
unlike in (1+1) dimensions, the energy density closely follows the longitudinal
pressure. The transverse momentum distribution of fermion pairs at large
momentum is quite different and larger than that expected from the constant
field result.
