Improved limit on the Ra 225 electric dipole moment

Background: Octupole-deformed nuclei, such as that of Ra225, are expected to amplify observable atomic electric dipole moments (EDMs) that arise from time-reversal and parity-violating interactions in the nuclear medium. In 2015 we reported the first "proof-of-principle" measurement of the Ra225 atomic EDM. Purpose: This work reports on the first of several experimental upgrades to improve the statistical sensitivity of our Ra225 EDM measurements by orders of magnitude and evaluates systematic effects that contribute to current and future levels of experimental sensitivity. Method: Laser-cooled and trapped Ra225 atoms are held between two high-voltage electrodes in an ultrahigh-vacuum chamber at the center of a magnetically-shielded environment. We observe Larmor precession in a uniform magnetic field using nuclear-spin-dependent laser light scattering and look for a phase shift proportional to the applied electric field, which indicates the existence of an EDM. The main improvement to our measurement technique is an order-of-magnitude increase in spin-precession time, which is enabled by an improved vacuum system and a reduction in trap-induced heating. Results: We have measured the Ra225 atomic EDM to be less than 1.4×10-23e cm (95% confidence upper limit), which is a factor of 36 improvement over our previous result. Conclusions: Our evaluation of systematic effects shows that this measurement is completely limited by statistical uncertainty. Combining this measurement technique with planned experimental upgrades, we project a statistical sensitivity at the 1×10-28e cm level and a total systematic uncertainty at the 4×10-29e cm level.