  We have investigated strange and charm quark-pair production in the early
stage of heavy ion collisions. Our kinetic model is based on a Wigner function
method for fermion-pair production in strong non-Abelian fields. To describe
the overlap of two colliding heavy ions we have applied the time-dependent
color field with a pulse-like shape. The calculations have been performed in an
SU(2)-color model with finite current quark masses. For strange quark-pair
production the obtained results are close to the Schwinger limit, as we
expected. For charm quark the large inverse temporal width of the field pulse,
instead of the large charm quark mass, determines the efficiency of the
quark-pair production. Thus we do not observe the expected suppression of charm
quark-pair production connecting to the usual Schwinger-formalism, but our
calculation results in a relatively large charm quark yield. This effect
appears in Abelian models as well, demonstrating that particle-pair production
for fast varying non-Abelian gluon field strongly deviates from the Schwinger
limit for charm quark. We display our results on number densities for light,
strange, charm quark-pairs, and different suppression factors as the function
of characteristic time of acting chromo-electric field.
