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

Abstract

We perform laser induced fluorescence(LIF) 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 3 ∆1 state. In particular, [20.6]Ω = 2, v ′ = 4 ← X 3 ∆1, v" = 0 transition at 485nm was used for the detection. The hyperfine structure and the Ω-doublet of the transition are 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 Ω-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 3 ∆1 state of WC molecule is discussed.

Zeeman interaction in ThOH3Δ1for the electron electric-dipole-moment search

“…Systematic effects related to magnetic field imperfections and geometric phases can still manifest themselves as a false EDM, though they are suppressed by a factor of ∼ g/g, where g is the gfactor difference between the two doublet states [5,14,22,23]. These systematics can be further suppressed by operating the experiment at an electric field where the g-factor difference is minimized [18,24] or where the g factors themselves are nearly canceled [25]; however, it is clear that understanding the g-factor dependence on electric fields is important for understanding possible systematic effects in polar-moleculebased eEDM searches. Additionally, measurement of g is a good test of an EDM measurement procedure [5,16].…”

“…This fact is explained by perturbations from the J = 2 level, as discussed in Refs. [18,21,24]. In turn, the nearest perturbing state for J = 2 is J = 1.…”

“…Polar molecules have a number of advantages over atoms for eEDM searches [10,11], including a larger E eff and resistance to a number of important systematics. Some molecules, for example, ThO [5,12], lead oxide (PbO) [13,14], HfF + [15,16], and WC [17,18], have additional advantages due to the existence of closely spaced levels of opposite parity, called an doublet. Molecules with doublets can typically be polarized in modest laboratory electric fields ( 1-100 V/cm), and in addition the spin-precession measurement can be carried out in a state where the molecular dipole is either aligned or antialigned with the external laboratory field.…”

“…In the framework of second-order perturbation theory for the g factors of the f and e states of H 3 1 , g f and g e , respectively, as functions of J in the absence of electric field we have [18,24] …”

Stimulated Raman adiabatic passage preparation of a coherent superposition of ThOH3Δ1states for an improved electron electric-dipole-moment measurement

“…This represents an order-of-magnitude improvement on the previous limits on d e [3,4]. Other measurements of d e are in preparation [5][6][7][8]. Related experiments measure nuclear [9] and neutron [10] electric-dipole moments.…”