"Low energy" probes of particle physics, which do not rely on producing high energy collisions in accelerators, are becoming increasingly important in searches for new physics beyond the Standard Model. These experiments can provide powerful tests of some of the most important outstanding problems in particle physics, including identifying the nature of dark matter and dark energy as well as the mechanism by which neutrinos acquire mass.
I will discuss two such experiments, both of which have the potential to observe beyond the Standard Model physics using low energy techniques. First, I will describe the Enriched Xenon Observatory (EXO), which is searching for neutrinoless double beta decay using large, liquid Xe time projection chambers. Observation of this lepton number violating decay would demonstrate that neutrinos are Majorana particles and could allow determination of the absolute neutrino mass scale. Second, I will discuss the development of sub-attonewton force sensors based on optically levitated dielectric microspheres in vacuum. This technique has the potential to revolutionize the search for new forces at micron length scales, probing large areas of previously unexplored parameter space in models that could explain the nature of dark matter, dark energy, or the microscopic properties of gravity. In both cases, I will describe recent results from existing experiments utilizing these techniques and prospects for next-generation searches for new physics.