Detection prospects of dark matter in the Einstein Telescope

We improve the calculations of the elastic motion induced by dark matter hitting the surface of the mirror inside an interferometer used for gravitational-wave detection. We focus on the discovery potential of such a dark matter signal in the third-generation European gravitational-wave detector, the Einstein Telescope. By taking the thickness of the mirror into account, more than one resonance is predicted in the sensitive regime of the high-frequency interferometer. When the mass of dark matter is heavier than a few PeV or is highly boosted, the signal-to-noise ratio could exceed one, and the Einstein Telescope should be able to detect this dark matter signal.