Tabletop detector for detecting dark massive particles with a crystal pendulum and laser doppler vibrometer.

The detectors of dark matter (DM) particles employ liquid noble gases, superheated liquid, crystals, etc. but DM is not yet directly detected. Galactic and extragalactic PeV-energy (10¹⁵ eV) gamma rays with zero rest masses are known. However, PeV mass-energy particles with non-zero rest mass have not yet been detected because of the lack of detectors for particles of approximately 100 times the total collision energy of the Large Hadron Collider. Here, we report an alternative detector for neutral massive particles (MP) of PeV energy by using a pendulum with a microgram crystalline bob. It does not need electromagnetic, nuclear, or chemical interaction between the detector and the particle. The linear momentum of PeV energy MP propagating with a cosmic speed of ~249 km/s is enough to start oscillations of such micro-pendulum. The amplitude and speed of crystal-bob oscillations are detected with a laser-doppler vibrometer. These data are compared with theoretical calculations of the amplitude of forced oscillations of the crystal-bob, which are initiated by a periodic force due to energetic MP hitting the crystal. It allows the estimate of the mass of these MP. In our experiments, this tabletop instrument detected MP from the Sun and the center of our galaxy. The detected solar MP-particles have average mass-energy of (3.1 ±1) ×10¹⁵ (eV/C²) = (5.5 ±1.8) ×10^-21 kg, which is several orders of magnitude bigger than a nucleon mass. The uncovered MP particles contribute to the masses of our galaxy and universe.