Probing scalar, Dirac, Majorana, and vector dark matter through a spin-0 electron-specific mediator at electron fixed-target experiments

We discuss the thermal target curves of Majorana, Dirac, scalar, and vector light dark matter (DM) that are associated with the freeze-out mechanism via the annihilation into the <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline"><a:msup><a:mi>e</a:mi><a:mo>+</a:mo></a:msup><a:msup><a:mi>e</a:mi><a:mo>−</a:mo></a:msup></a:math> pair through the electron-specific spin-0 mediator of dark matter. We also discuss the mechanism to produce the regarded DM mediator in the electron (positron) fixed-target experiments such as NA64e and LDMX. We derive the corresponding experimental reaches of NA64e and LDMX that are complementary to the DM thermal target parameter space.