Improved isotope-shift-based bounds on bosons beyond the Standard Model through measurements of the $^2$D$_{3/2} - ^2$D$_{5/2}$ interval in Ca$^+$

TL;DR

This study uses high-precision spectroscopy of calcium ions to improve bounds on hypothetical bosons beyond the Standard Model by analyzing isotope shifts and conducting a King plot analysis, with implications for other ions like Ba+ and Yb+.

Contribution

The paper introduces highly accurate isotope shift measurements in Ca+ ions and applies a King plot analysis to set new constraints on electron-neutron couplings to beyond-Standard-Model bosons.

Findings

Enhanced sensitivity to new bosons through isotope shift analysis.

Established tighter bounds on electron-neutron couplings.

Provided precise isotope shift data for Ca+ transitions.

Abstract

We perform high-resolution spectroscopy of the $3$d$~^2$D$_{3/2} - 3$d$~^2$D$_{5/2}$ interval in all stable even isotopes of $^A$Ca$^+$ (A = 40, 42, 44, 46 and 48) with an accuracy of $\sim$ 20 Hz using direct frequency-comb Raman spectroscopy. Combining these data with isotope shift measurements of the 4s$~^2$S$_{1/2} \leftrightarrow 3$d$~^2$D$_{5/2}$ transition, we carry out a King plot analysis with unprecedented sensitivity to coupling between electrons and neutrons by bosons beyond the Standard Model. Furthermore, we estimate the sensitivity to such bosons from equivalent spectroscopy in Ba$^+$ and Yb$^+$. Finally, the data yield isotope shifts of the 4s$~^2$S$_{1/2} \leftrightarrow 3$d$~^2$D$_{3/2}$ transition at 10 part-per-billion through combination with recent data of Knollmann et al (2019).