Global analysis of CP-violation in atoms, molecules and role of medium-heavy systems

Abstract

Detection of parity P and time-reversal T symmetry-odd electric dipole moments (EDMs) within currently achievable resolution would evidence physics beyond the Standard Model of particle physics. Via the CPT-theorem, which includes charge conjugation C, such low-energy searches complement high-energy physics experiments that probe CP-violation up to the TeV scale. Heavy-elemental atoms and molecules are considered to be among the most promising candidates for a first direct detection of P, T-violation due to enhancement effects that increase steeply with increasing nuclear charge number Z. However, different P, T-odd sources on the subatomic level can contribute to molecular or atomic EDMs, which are target of measurements, and this complicates obtaining rigorous bounds on P, T-violation on a fundamental level. Consequently, several experiments of complementary sensitivity to these individual P, T-odd sources are required for this purpose. Herein, a simply-applicable qualitative model is developed for global analysis of the P, T-odd parameter space from an electronic-structure theory perspective. Rules of thumb are derived for the choice of atoms and molecules in terms of their angular momenta and nuclear charge number. Contrary to naive expectations from Z-scaling laws, it is demonstrated that medium-heavy molecules with Z ≤ 54 can be of great value to tighten global bounds on P, T-violating parameters, in particular, if the number of complementary experiments increases. The model is confirmed by explicit density functional theory calculations of all relevant P, T-odd electronic structure parameters in systems that were used in past experiments or are of current interest for future experiments, respectively: the atoms Xe, Cs, Yb, Hg, Tl, Ra, Fr and the molecules CaOH, SrOH, YO, CdH, BaF, YbF, YbOH, HfF+, WC, TlF, PbO, RaF, ThO, ThF+ and PaF3+.