Optical spectroscopy of tungsten carbide for uncertainty analysis in electron electric-dipole-moment search

Abstract

We perform laser-induced fluorescence spectroscopy on a pulsed supersonic beam of tungsten carbide (WC) molecules, which has been proposed as a candidate molecular system for a permanent electric dipole moment (EDM) search of the electron in its rovibrational ground state of the $X\phantom{\rule{0.16em}{0ex}}{}^{3}{\ensuremath{\Delta}}_{1}$ state. In particular, $[20.6]\ensuremath{\Omega}=2,{v}^{\ensuremath{'}}=4\ensuremath{\leftarrow}X\phantom{\rule{0.16em}{0ex}}{}^{3}{\ensuremath{\Delta}}_{1},{v}^{\ensuremath{'}\ensuremath{'}}=0$ transition at 485 nm was used for the detection. The hyperfine structure and the $\ensuremath{\Omega}$ doublet of the transition is measured, which are essential for estimating the size of the potential systematic uncertainties for electron EDM measurement. For further suppression of the systematic uncertainty, an alternative electron EDM measurement scheme utilizing the $g$ factor crossing point of the $\ensuremath{\Omega}$-doublet levels is discussed. On the other hand, flux and internal temperature of the molecular beam are characterized, which sets the limit on the statistical uncertainty of the electron EDM experiment. With the given results, the prospect of electron EDM experiment with the $X\phantom{\rule{0.16em}{0ex}}{}^{3}{\ensuremath{\Delta}}_{1}$ state of WC molecule is discussed.