Enhanced spin-dependent parity non-conservation effect in the $7s {}^2S_{1/2} \to 6d {}^2D_{5/2}$ transition in Fr: A possibility for unambiguous detection of nuclear anapole moment

TL;DR

This study predicts a significantly enhanced parity non-conservation effect in francium isotopes' specific atomic transition, offering a promising method for detecting the nuclear anapole moment through measurable light shifts.

Contribution

It demonstrates that electron core-polarization effects greatly amplify PNC amplitudes in francium, enabling potential unambiguous detection of the nuclear anapole moment.

Findings

PNC electric dipole amplitudes are over 1000 times larger in Fr than in Ba+ and Ra+.

Enhanced effects are due to large electron core-polarization contributions.

Proposed measurement scheme at Tohoku University's CYRIC facility.

Abstract

Employing the relativistic coupled-cluster method, comparative studies of the parity non-conserving electric dipole amplitudes for the $7s \ ^2S_{1/2} \rightarrow 6d \ ^2D_{5/2}$ transitions in $^{210}$Fr and $^{211}$Fr isotopes have been carried out. It is found that these transition amplitudes, sensitive only to the nuclear spin dependent effects, are enhanced by more than 3 orders compared to the low-lying $S-D_{5/2}$ transitions in Ba$^+$ and Ra$^+$ owing to the very large contributions from the electron core-polarization effects in Fr. This translates to a relatively large and, in principle, measurable induced light shift, which would be a signature of nuclear spin dependent parity nonconservation that is dominated by the nuclear anapole moment in a heavy atom like Fr. A plausible scheme to measure this quantity using the Cyclotron and Radioisotope Center (CYRIC) facility at Tohoku University has been outlined.