Electrostatic focusing of cold and heavy molecules for the ACME electron EDM search

Measurements of the electron electric dipole moment (EDM) using atoms and molecules shed light on T-symmetry violating new physics beyond the Standard Model. The best upper limit on the electron EDM was recently set by the ACME collaboration: |d_e|<1.1×10^-29 e·cm (Nature, 562, 355 (2018)), using a cold beam of heavy molecules, thorium monoxide (ThO). This result significantly constrains T-violating new physics in the 1∼10 TeV range and above. Upgrades to a new generation ACME measurement are now underway. Here, we report the demonstration of electrostatic focusing of ThO with a hexapole lens, resulting in over 16× enhancement in the molecular flux arriving at the electron EDM detection region. While preparing ThO into a single quantum state for the beam focusing, we demonstrate an upgraded rotational cooling protocol that increases the ground state population by a factor of 3.5, consistent with the theoretical limit. This is 1.4× improvement compared to the previous schemes. When combined with other improvements, we project over an order of magnitude improvement in the statistical sensitivity for the next generation ACME electron EDM search.