  We discuss the mechanism to produce electron-specific dark matter mediators
of spin-0 and spin-2 in the electron fixed target experiments such as NA64 and
LDMX. The secondary positrons induced by the electromagnetic shower can produce
the mediators via annihilation on atomic electrons. That mechanism, for some
selected kinematics, results in the enhanced sensitivity with respect to the
bounds derived by the bremsstrahlunglike emission of the mediator in the
specific parameter space. We derive the corresponding experimental reach of the
NA64 and LDMX.
