Model-independent determinations of the electron EDM and the role of diamagnetic atoms

TL;DR

This paper conducts model-independent analyses to set limits on the electron EDM and P,T-odd couplings using recent atomic and molecular measurements, highlighting the role of diamagnetic atoms and hyperfine interactions.

Contribution

It introduces a new method for calculating hyperfine-induced P,T-odd effects in diamagnetic atoms, improving constraints on fundamental CP-violating parameters.

Findings

First direct calculation of S-PS coupling in diamagnetic Hg atom.

Improved limits on electron EDM and nucleon-electron coupling from combined data.

Demonstrates the importance of diamagnetic atoms in constraining fundamental symmetries.

Abstract

We perform model-independent analyses extracting limits for the electric dipole moment of the electron and the P,T-odd scalar-pseudoscalar (S-PS) nucleon-electron coupling from the most recent measurements with atoms and molecules. The analysis using paramagnetic systems, only, is improved substantially by the inclusion of the recent measurement on HfF+ ions, but complicated by the fact that the corresponding constraints are largely aligned, owing to a general relation between the coefficients for the two contributions. Since this same relation does not hold in diamagnetic systems, it is possible to find atoms that provide essentially orthogonal constraints to those from para\-magnetic ones. However, the coefficients are suppressed in closed-shell systems and enhancements of P,T-odd effects are only prevalent in the presence of hyperfine interactions. We formulate the hyperfine-induced time-reversal-symmetry breaking S-PS nucleon-electron interaction in general atoms in a mixed perturbative and variational approach, based on electronic Dirac-wavefunctions including the effects of electron correlations. The method is applied to the Hg atom, yielding the first direct calculation of the coefficient of the S-PS nucleon-electron coupling in a diamagnetic system. This results in additionally improved model-independent limits for both the electron EDM and the nucleon-electron coupling from the global fit. Finally we employ this fit to provide indirect limits for several paramagnetic systems under investigation.