Enhanced Sensitivity to the Time Variation of the Fine-Structure Constant and $m_p/m_e$ in Diatomic Molecules: A Closer Examination of Silicon Monobromide

TL;DR

This paper investigates silicon monobromide's potential for detecting variations in fundamental constants by analyzing its rovibronic spectrum with experimental data and ab initio calculations, considering linewidth limitations.

Contribution

It provides a detailed analysis of SiBr's spectrum and sensitivity to fundamental constant variations, including linewidth estimates, advancing the use of diatomic molecules in fundamental physics tests.

Findings

SiBr shows enhanced sensitivity to variations in $\alpha$ and $m_p/m_e$

Accurate spectral dependence on fundamental constants established

Natural linewidths limit measurement precision

Abstract

Recently it was pointed out that transition frequencies in certain diatomic molecules have an enhanced sensitivity to variations in the fine-structure constant $\alpha$ and the proton-to-electron mass ratio $m_p/m_e$ due to a near cancellation between the fine-structure and vibrational interval in a ground electronic multiplet [V.~V.~Flambaum and M.~G.~Kozlov, Phys. Rev. Lett.~{\bf 99}, 150801 (2007)]. One such molecule possessing this favorable quality is silicon monobromide. Here we take a closer examination of SiBr as a candidate for detecting variations in $\alpha$ and $m_p/m_e$. We analyze the rovibronic spectrum by employing the most accurate experimental data available in the literature and perform \emph{ab initio} calculations to determine the precise dependence of the spectrum on variations in $\alpha$. Furthermore, we calculate the natural linewidths of the rovibronic levels, which place a fundamental limit on the accuracy to which variations may be determined.