Searching for BSM physics with low-energy bound states: spin-polarized atoms and neutrons

• Skyler Degenkolb

I will introduce two complementary approaches for performing precision measurements with spin-polarized quantum systems: time-domain interferometry using stored ultracold neutrons, and the continuous observation of nuclear-spin comagnetometers. Both are motivated by the quest to measure finite permanent electric dipole moments (EDMs), an expected signature of the CP-violating new physics that is needed to explain the cosmological matter-antimatter asymmetry. In contrast to direct searches EDMs act like a "lightning rod", gathering the signatures of numerous effective sources into a single observable with negligible background from the Standard Model. Recent technological innovations have led to measurements with improved sensitivity [1] and new proposals [2], extending certain constraints on new degrees of freedom above the TeV mass scale. I will discuss these approaches as a means of establishing joint constraints on CP-violating effective couplings in hadronic systems, and outline the prospects for further experimental improvements. The application of quantum sensing methods for this type of precision measurement is a focus of the new research group 'Low Energy Precision Physics' at Heidelberg University's Physikalisches Institut. [1] N. Sachdeva et al., Phys. Rev. Lett. 123, 143003 (2019) [2] D. Wurm et al., EPJ Web of Conferences 219, 02006 (2019)