The Most Precise Measurement Of The Shape Of The Field Around An Electron

• Researchers find signatures of exotic particles that aren’t explained in the standard model of physics.
• They showed that field around an electron spontaneously transform into new particles. 

In the Standard Model of particle physics, electrons are negatively charged subatomic particles that exist in atoms’ spherical shells of different radii, representing energy levels. The bigger the spherical shell, the higher the energy electrons contain. Although they are extremely small, they can help us understand theories of how the universe works.

Recently, a research team at Harvard University precisely measured the shape of the field around an electron, and the outcomes indicate that a few theories that explain what lies beyond the standard model may have to be reevaluated.

This is the best measurement researchers have come across till date. It has emerged from a 10-year long project, named ACME (advanced cold molecule electron electric dipole moment) search, for finding signatures of exotic particles that aren’t explained in the standard model of physics.

Electron Dipole Moment

The two major observations that aren’t explained by the standard model are:

1. Matter-antimatter asymmetry in the Universe
2. Dark matter

At the absolute beginning of the time (zero to 10^-43 seconds, or Planck Era), the universe was an extremely hot and small place where matters and antimatter were present in equal amounts. One second after the Big Bang, the universe was filled with photons, protons, electrons, anti-electrons, neutrons, and neutrinos.

There’s a general theory that explains how stars, planets, skies, etc. formed. That theory requires a phenomenon known as ‘Time Reversal Violation’, according to which microscopic physics can determine in which direction time is flowing. However, the standard model doesn’t contain enough data to explain this.

The other mysterious thing is dark matter: We can see it by observing the light’s direction as it passes through galaxies. Based on galaxy discs’ rotation frequencies, scientists know there must be something driving this, but they don’t know yet what it is exactly.

There are numerous theories that explain the matter-antimatter asymmetry by predicting new particles in the universe. Some of those predicted particles are considered as candidates of dark matter.

Though many scientists are using Large Hadron Collider to study these new particles, the authors have used a large-office-sized instrument to study the ‘electron dipole moment’ – an evidence that shows field around an electron is spontaneously converting into predicted particles.

According to the researchers, there is a dance constantly going on between the field and the particle: the field is being transformed into a particle that decays back into the field.

Reference: Nature | doi:10.1038/s41586-018-0599-8 | Harvard University 

To observe this effect, researchers referred to these predicted particles as ‘virtually created’ particles. They make electrons look like a molecule with a tiny positive and negative charge on each end. The electron with a field isn’t completely spherical, but quite squashed.

How Did They Do It?

Image credit: Stephen Alvey/Michigan Engineering

To make this happen, researchers fired a beam (containing cold molecules of thorium-oxide) into a little chamber where lasers choose certain quantum states. This changes the orientation of both molecules and electrons as lasers pass between 2 charged plates within a supervised magnetic field.

A different group of ‘readout’ lasers focuses on molecules coming out of the chamber, making them emit light. One can detect whether the electrons tumble or twist during flight, by observing this light.

In this study, researchers reported that they didn’t observe any electron dipole moment. This indicates that new particles would have different characteristics than what was anticipated. Thus, theories explaining beyond-standard-model particles may require a serious revaluation.

Read: The World’s Coldest Nanoelectronic Chip | 2.8 milliKelvin

Although the study does not explains what exactly lies beyond the standard model, it is surely worthwhile to keep making efforts.