The repeated measurements of neutrino oscillations over the last few decades confirm that neutrinos have non-zero masses which are not accounted for in the Standard Model. The observed small neturino masses can be explained by introducing a massive right-handed "sterile neutrino" that does not interact through the weak force. One class of experiments searching for sterile neutrinos utilise radioactive decays to generate neutrinos and search for deviations in the recoil energy spectra of the daughter nucleus that would suggest mixing between Standard Model neutrinos and a sterile neutrino. We present a new experiment that is currently being realised that utilises levitated nanoparticles doped with a radioactive isotope to measure the momentum of the recoiling daughter nucleus and reconstruct the momentum of the emitted neutrino. Measuring momentum rather than energy significantly reduces the impact of low or zero mass backgrounds and secondary emissions. This search will improve sensitivity to sterile neutrinos in the mass range 100 keV - 2 MeV compared to previous experiments.
Recent development in levitated optomechanics has presented new detection platforms for a diverse range of dark matter candidates. We discuss our recent application of using a nanogram-scale silica microparticle optically trapped in high vacuum to search for impulse signals induced by passing composite dark matter. The search is enabled by the achieved ~ 100 MeV/c momentum sensitivity of the system and the ability to stably trap and cool down micron-size particles. We also discuss our recent progress in constructing an array of levitated sensors and searching in the new parameter space with levitated nanoparticles.
Highly sensitive levitated optomechanical systems can be used as precise acceleration and force sensors to search for fundamental physics. Eliminating the net charge on these systems reduces the most significant coupling to external electric fields yet leaves the issue of backgrounds created by higher order multipole moments in the charge distribution of the levitated sensors. In many high sensitivity applications of levitated optomechanical sensors, dipole induced forces can be many orders of magnitude larger than the forces of interest. Thus, techniques to measure, control, and ultimately eliminate dipole generated backgrounds may be required to realize numerous experiments such as the search for millicharged particles, the exploration of new parameter space of dark matter mass with an array of levitated microspheres and possibly future work towards detection of gravitational entanglement between micron sized masses. This talk will discuss the application of controlled precessive torques to the electric dipole moment of a levitated microsphere in vacuum to reduce dipole-induced backgrounds by 2 orders of magnitude as well as work towards integrating such sensors in large arrays.
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