The Dark Matter elusiveness could be explained by speculating that it lives in a separate sector with respect to the Standard Model(SM)and that interacts with it only by means of messengers. The simplest model foresees just one messenger: a possibly massive vector boson given by a new U(I)symmetry. This mediator can faintly mix with the photon and, hence, interact with SM charged particles, seeing an effective charge equal to ε?e, but also the production of axion-like particles or dark scalars can be explored. In searching such mediators at accelerators, the fixed-target approach is favored over colliding beams because of the higher luminosity; among the different classes of experiment the e~+e~-annihilation is the less model-dependent approach, and has the potential of positively identifying new particles, regardless from its final state. Producing high-energy, high-intensity positron pulses from a LINAC or extracting them from a e~+ ring have been both considered: the different available time structure, repetition rate, maximum energy and beam intensity reflect in different sensitivities for dark sector searches, a panorama of the available facilities in Italy and USA is given.
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