The Standard Model of particle physics is one of the greatest achievements of modern science. It has been fabulously successful in classifying the fundamental particles and explaining how they behave. Nevertheless, it is widely accepted that the Standard Model is incomplete because it fails to explain several important observations. One prominent example is the excess of matter over antimatter in the universe. The Standard Model predicts almost equal amounts of matter and antimatter, but observations show the universe contains only matter. This contradiction is one of the great unsolved problems in modern physics and a major deficiency of our most fundamental theory.

To build a more complete picture of the universe, physicists are striving to reveal what lies beyond the Standard Model. This is an important objective of much of the research being done at gigantic particle accelerators. There is an alternative, and ingenious, way to explore the same problem – measure the shape of an electron. The new forces needed to explain the matter/antimatter imbalance also make electrons slightly non-spherical. This distortion–known as the electric dipole moment (EDM)–changes the energy of an electron in an electric field, and that tiny change is amplified when the electron is bound to a molecule. The research team has been building an apparatus that uses an array of molecules cooled to microkelvin temperatures to make an extremely precise measurement of the electron’s shape. With very careful measurements, such table-top experiments enable us to probe energies equal to, or even above, those reached by the particle accelerators.

In the Centre for Cold Matter there are two experiments to measure the EDM:

  1. Ultracold eEDM Experiment: This experiment aims to use a molecular beam of YbF molecules cooled to ultracold temperatures, which allows for longer spin-precession times and more precise measurements. Techniques involving buffer-gas beams and laser cooling are employed to achieve the required low temperatures. Spin polarizing and readout methods are adapted for spatially and temporally long molecular beams.

  2. Lattice eEDM Experiment: This experiment utilizes YbF molecules in a 3D optical lattice, requiring laser cooling to ultracold temperatures and subsequent trapping and cooling in all three dimensions. Techniques such as buffer-gas molecular beams and laser slowing are employed to achieve the necessary slow speeds for trapping and cooling. The aim is to achieve even longer spin-precession times and more precise measurements compared to previous experiments.

Find out more

You can find out more on our project page Electron edm


For more information, please contact Dr. Jongseok Lim (j.lim@imperial.ac.uk), Prof. Ben Sauer (ben.sauer@imperial.ac.uk) or Prof. Mike Tarbutt (m.tarbutt@imperial.ac.uk