Session K06: Focus Session: Advances in EDMs with Molecules

Precision dipole measurements in trapped molecular ions: recent results and future prospects

The Standard Model or particle physics predicts undetectably small electric dipole moments in fundamental particles. An experimental observation of such a moment would be a compelling signature of new physics. Molecular ions can offer both large internal electric fields and long coherence times, and are thus promising systems for dipole-moment searches. We report on recent results from JILA and prospects for future improvement.   

Probing new physics using trapped molecular ions: JILA's electron EDM search

Precision measurement of fundamental asymmetries, such as the electron's electric dipole moment (eEDM), can help to probe physics beyond the standard model and explore mysteries such as dark matter or the baryon asymmetry. Trapped molecular ions can be remarkably sensitive to small effects such as an electron EDM while offering robust rejection of systematics. Our approach at JILA takes advantage of the large internal electric fields in a molecule, and the long coherence times possible with trapped ions. In this talk, I will provide an overview of our second-generation EDM measurement, focusing on current demonstrations and future plans to improve our sensitivity by an order of magnitude.   

Progress Towards an Order of Magnitude Improved ACME II Measurement of the Electron Electric Dipole Moment

The search for the electron electric dipole moment (eEDM) is a powerful probe of physics beyond the Standard Model. In 2014, the first generation of the ACME experiment set the most stringent upper limit on the eEDM of $|d_e|<0.9\times10^{-28}$ e$\cdot$cm by measuring spin precession in a beam of thorium monoxide (Science \textbf{343} (2014), 269). Since then, we have implemented improvements in signal, such as STIRAP preparation of the experimental measurement $^3\Delta_1$ state, optimized apparatus geometry, and enhanced detection efficiency, which have increased our statistical sensitivity by an order of magnitude (Phys. Rev. A \textbf{93} (2016), 052110). We describe recent progress in the ACME II measurement, including a discussion of data analysis and modeling and suppression of systematic errors.   

Precision measurements with laser-cooled polyatomic molecules

Polar molecules are extremely sensitive platforms to search for physics Beyond the Standard Model, especially CP-violating electromagnetic moments that are amplified by large internal molecular fields. Molecule-based searches for the electron EDM are already probing the TeV scale, and their strong robustness against systematic errors via internal co-magnetometer states means that they can reach even higher energy scales in a variety of sectors. Molecule precision measurements are currently limited largely by interaction time, and could be enhanced by many orders of magnitude if suitable molecules could be cooled and trapped like their atomic counterparts. Laser-cooling of molecules is advancing rapidly, but current techniques only work for molecules with particular electronic structures that conflict with the requirements for internal co-magnetometers in diatomic molecules. However, polyatomic molecules (with at least three atoms) have mechanical modes that can be used to realize internal co-magnetometer states, while still offering the electronic structure required for laser-cooling [1]. Polyatomic molecules such as YbOH and YbOCH3 are therefore candidates for long coherence time precision measurements of CP-violation at the PeV scale with laser-cooling, trapping, and internal co-magnetometers. We will discuss the interesting physics of laser cooling and polyatomic molecules that makes this possible, and present an update on experimental progress. [1] I. Kozyryev and N. R. Hutzler, Phys. Rev. Lett. 119, 133002 (2017)   

Measuring the electron-EDM using a slow, intense and cold beam of BaF molecules

We have started a program to perform a measurement of the permanent electric dipole moment of the electron (eEDM) with barium monofluoride molecules, thereby searching for phenomena of CP violation beyond those incorporated in the Standard Model of particle physics. Although the BaF molecule has a smaller internal electric field enhancement factor than other molecules used in current studies (YbF, ThO and ThF$^+$), we exploit the possibilities to Stark-decelerate and laser-cool this species, combined with an intense primary cold source of BaF molecules. With the resulting long coherent interaction times obtainable in a cold beam of BaF, we aim to reach a competitive sensitivity for an eEDM in this first generation experiment. In this contribution we describe the rationale, the challenges and the experimental methods envisioned to achieve this target.   

Upgrades for an Improved Measurement of the EDM of Ra-225

A non-zero Electric Dipole Moment (EDM) in a non-degenerate system violates time-reversal (T) symmetry and therefore charge-parity (CP) symmetry due to the CPT theorem. EDM measurements are therefore sensitive and background-free searches for new CP violating interactions. Ra-225, with its octupole deformation and nearly degenerate nuclear parity doublet, is an extremely attractive candidate for probing CP violations in the hadronic sector. Our latest measurement limits the EDM of Ra-225 to be less than 1.4x10$^{\mathrm{-23}}$ e-cm (95{\%} C.L.), and is the first ever measurement of an EDM limit using laser cooled and trapped atoms. Further experimental upgrades are being implemented including an electric field upgrade to enhance the EDM sensitivity and STIRAP-based electron shelving for improved state detection efficiency. With these upgrades in place our EDM sensitivity should increase by about two orders of magnitude and allow us to substantially improve constraints on certain T-violating processes within the nucleus. Updates on the status of these upgrades will be provided. This work is supported by the U.S. DOE, Office of Science, Office of Nuclear Physics, under contract DE-AC02-06CH11357 and the Michigan State University.