Beam dump experiment at future electron–positron colliders

We propose a new beam dump experiment at future colliders with electron (e−e−) and positron (e+e+) beams, BDee  , which will provide a new possibility to search for hidden particles, like hidden photon. If a particle detector is installed behind the beam dump, it can detect the signal of in-flight decay of the hidden particles produced by the scatterings of e±e± beams off materials for dumping. We show that, compared to past experiments, BDee (in particular BDee   at e+e−e+e− linear collider) significantly enlarges the parameter region where the signal of the hidden particle can be discovered.