Systematic study and uncertainty evaluation of P, T-odd molecular enhancement factors in BaF

Abstract

A measurement of the magnitude of the electric dipole moment of the electron (eEDM) larger than that predicted by the Standard Model (SM) of particle physics is expected to have a huge impact on the search for physics beyond the SM. Polar diatomic molecules containing heavy elements experience enhanced sensitivity to parity (P) and time-reversal (T)-violating phenomena, such as the eEDM and the scalar-pseudoscalar (S-PS) interaction between the nucleons and the electrons, and are thus promising candidates for measurements. The NL-eEDM collaboration is preparing an experiment to measure the eEDM and S-PS interaction in a slow beam of cold BaF molecules [P. Aggarwal et al., Eur. Phys. J. D 72, 197 (2018)]. Accurate knowledge of the electronic structure parameters, W d and Ws, connecting the eEDM and the S-PS interaction to the measurable energy shifts is crucial for the interpretation of these measurements. In this work, we use the finite field relativistic coupled cluster approach to calculate the W d and Ws parameters in the ground state of the BaF molecule. Special attention was paid to providing a reliable theoretical uncertainty estimate based on investigations of the basis set, electron correlation, relativistic effects, and geometry. Our recommended values of the two parameters, including conservative uncertainty estimates, are 3.13 ± 0.12 × 10 24 Hz e cm for W d and 8.29 ± 0.12 kHz for Ws.

The role of QED effects in transition energies of heavy-atom alkaline earth monofluoride molecules: a theoretical study of Ba$^+$, BaF, RaF and E120F

“…For this, we have performed scalar-relativistic (SR) CCSD(T) calculations within the X2C approach 70 and correlating 27 outer electrons. The extended basis set LBa-sExt [39,33,26,37,11,10,8] has been obtained from the LBas basis set by adding several g−, h− and i− type functions and replacement of f − type function by an even-tempered set. As one can see from Table I basis set extension correction is small.…”

“…At present, a few experiments on the barium monofluoride molecule, BaF, have been proposed. It is suggested to measure the electron electric dipole moment using BaF and thus test different models of new physics which imply violation of both spatial parity (P) and time-reversal (T) symmetries [3][4][5][6][7][8] . Another suggestion is to experimentally study P-odd and T-even effects.…”

Benchmarking of the Fock space coupled cluster method and uncertainty estimation: Magnetic hyperfine interaction in the excited state of BaF

“…c. Higher-order excitations In the 2 Σ 1/2 ground state the error due to the missing triple and higher excitation is estimated by taking half the difference between CCSD(T) and CCSD, similar to our previous works [5,8,26,45,46]. The factor 1/2 is justified by the small spread in the results obtained with different treatment of perturbative triples.…”

“…Such benchmarks of ab initio methods, carried out on measurable properties, also serve to confirm the accuracy of the approach for properties where no experiment is yet possible. For example, in case of BaF, such properties are the P, T -odd molecular enhancement factors, W s and W d [8], which are crucial for the interpretation of the NL-eEDM experiment [7], or the W A factor [9], needed for extracting the nuclear anapole moment from future measurements [10]. BaF is particularly interesting for precision experiments due to, among other things, its good laser cooling properties [11][12][13].…”

Doppler cooling of buffer-gas-cooled Barium monofluoride molecules

“…Barium monofluoride (BaF) molecule has been considered as an attractive candidate for laser cooling for various reasons [23][24][25]. It is a heavy molecule, has a very high sensitivity for measuring the electric dipole moment (EDM) [26,27], and parity violation [28][29][30][31]. Once it can be cooled and trapped, the accuracy of those measurements will be improved significantly.…”