  Particle production from an expanding classical color electromagnetic field
is extensively studied, motivated by the early stage dynamics of
ultra-relativistic heavy ion collisions. We develop a formalism at one-loop
order to compute the particle spectra by canonically quantizing quark, gluon
and ghost fluctuations under the presence of such an expanding classical color
background field; the canonical quantization is done in the $\tau$-$\eta$
coordinates in order to take into account manifestly the expanding geometry. As
a demonstration, we model the expanding classical color background field by a
boost-invariantly expanding homogeneous color electric field with lifetime $T$,
for which we obtain analytically the quark and gluon production spectra by
solving the equations of motion of QCD non-perturbatively with respect to the
color electric field. In this paper we study (i) finite lifetime effect which
is found to modify significantly the particle spectra from those expected from
the Schwinger formula; (ii) the difference between the quark and gluon
production; and (iii) the quark mass dependence of the production spectra.
Implications of these results to ultra-relativistic heavy ion collisions are
also discussed.
