Measurement of the nuclear Schiff moment of ¹⁵³Eu: systematic error tests

A nuclear Schiff moment (NSM) is a property of a nuclear charge distribution that breaks parity (P) and time-reversal (T) symmetries. Measurable NSMs are produced by T-violating physics beyond the Standard Model, and therefore the measurement of an NSM can be used to search for new physics at extremely high energy scales beyond the reach of colliders. We performed a measurement of the NSM of the ¹⁵³Eu nucleus, using Eu³⁺ ions in a yttrium orthosilicate (YSO) crystal. In this system, a large NSM is predicted to be generated by T-violating new physics, and the effect of the NSM is further enhanced by the polarized Eu³⁺ ions in the crystal. We performed precision measurements of nuclear spin resonances -- simultaneously in two oppositely-polarized ensembles of Eu³⁺ ions -- and compared these resonance frequencies to extract the P-odd T-odd NSM. We will present the details of these measurements, focusing on tests of systematic errors conducted with an extended dataset.