Intense slow beams of heavy molecules to test fundamental symmetries

Slow molecular beams allow for a very sensitive test of the Standard Model of particle physics. We are particularly interested in measuring the electron electric dipole moment (eEDM) in heavy diatomic polar molecules. The precision of these measurements is limited by the statistical measurement uncertainty. To minimize the latter, we build a cryogenic buffer gas source that produces slow intense beams of SrF (strontium fluoride) molecules. The molecules are further decelerated with a 4.5-meter-long Stark decelerator. After transverse laser-cooling the beam, a very sensitive eEDM measurement can be performed in the future

High accuracy theoretical investigations of CaF, SrF, and BaF and implications for laser-cooling

The NL-eEDM collaboration is building an experimental setup to search for the permanent electric dipole moment of the electron in a slow beam of cold barium fluoride molecules [Eur. Phys. J. D, 72, 197 (2018)]. Knowledge of molecular properties of BaF is thus needed to plan the measurements and in particular to determine an optimal laser-cooling scheme. Accurate and reliable theoretical predictions of these properties require incorporation of both high-order correlation and relativistic effects in the calculations. In this work theoretical investigations of the ground and the lowest excited states of BaF and its lighter homologues, CaF and SrF, are carried out in the framework of the relativistic Fock-space coupled cluster (FSCC) and multireference configuration interaction (MRCI) methods. Using the calculated molecular properties, we determine the Franck-Condon factors (FCFs) for the $A^2\Pi_{1/2} \rightarrow X^2\Sigma^{+}_{1/2}$ transition, which was successfully used for cooling CaF and SrF and is now considered for BaF. For all three species, the FCFs are found to be highly diagonal. Calculations are also performed for the $B^2\Sigma^{+}_{1/2} \rightarrow X^2\Sigma^{+}_{1/2}$ transition recently exploited for laser-cooling of CaF; it is shown that this transition is not suitable for laser-cooling of BaF, due to the non-diagonal nature of the FCFs in this system. Special attention is given to the properties of the $A'^2\Delta$ state, which in the case of BaF causes a leak channel, in contrast to CaF and SrF species where this state is energetically above the excited states used in laser-cooling. We also present the dipole moments of the ground and the excited states of the three molecules and the transition dipole moments (TDMs) between the different states.Comment: Minor changes; The following article has been submitted to the Journal of Chemical Physics. After it is published, it will be found at https://publishing.aip.org/resources/librarians/products/journals

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

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, Wd 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 Wd 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 ±0.12×1024Hzecm for Wd and 8.29 ± 0.12 kHz for W

Intense slow beams of heavy molecules to test fundamental symmetries

Slow molecular beams allow for a very sensitive test of the Standard Model of particle physics. We are particularly interested in measuring the electron electric dipole moment (eEDM) in heavy diatomic polar molecules. The precision of these measurements is limited by the statistical measurement uncertainty. To minimize the latter, we build a cryogenic buffer gas source that produces slow intense beams of SrF (strontium fluoride) molecules. The molecules are further decelerated with a 4.5-meter-long Stark decelerator. After transverse laser-cooling the beam, a very sensitive eEDM measurement can be performed in the future

Search for a permanent electric dipole moment on the electron (eEDM) using BaF molecules

As the NL-eEDM collaboration, we are searching for a permanent electric dipole moment on the electron (eEDM) in a BaF molecular beam. In preperation of such an experiment we have performed spectroscopic measurements in a supersonic BaF beam. The lifetimes of the A21/2 and A23/2 states were obtained using short light pulses generated from a CW laser beam with a pulsed acousto-optic modulator. An eEDM search in BaF puts stringent requirements on the fields in an interaction zone. Those include an electric field of O(10 kV/cm) and a magnetic field of O(10 nT), both with small field gradients i.e. less than 1% inhomogeneity. We are currently building the interaction zone to work with the intense supersonic BaF beam. Ultimately the sensitivity can be improved with a substantially decelerated and laser-cooled BaF molecular beam. In our experiment we aim at an eEDM sensitivity down to 5 × 10−30 e cm

Search for a permanent electric dipole moment on the electron (eEDM) using BaF molecules

As the NL-eEDM collaboration, we are searching for a permanent electric dipole moment on the electron (eEDM) in a BaF molecular beam. In preperation of such an experiment we have performed spectroscopic measurements in a supersonic BaF beam. The lifetimes of the A21/2 and A23/2 states were obtained using short light pulses generated from a CW laser beam with a pulsed acousto-optic modulator. An eEDM search in BaF puts stringent requirements on the fields in an interaction zone. Those include an electric field of O(10 kV/cm) and a magnetic field of O(10 nT), both with small field gradients i.e. less than 1% inhomogeneity. We are currently building the interaction zone to work with the intense supersonic BaF beam. Ultimately the sensitivity can be improved with a substantially decelerated and laser-cooled BaF molecular beam. In our experiment we aim at an eEDM sensitivity down to 5 × 10−30 e cm