When learning the basics of atomic structure in school, we all pictured electrons as perfectly round. That’s just easier than pondering the ramifications of dark matter on the Standard Model. Scientists have long wondered just how round electrons are, an answer that could affect how we understand subatomic particles. The most precise model of the electron yet has now demonstrated that your science teacher was right — electrons are almost perfectly round, and that’s going to make some physicists very unhappy.
It’s impossible with current technology to image subatomic particles directly, but we can model them by examining indirect evidence. This is important because the shape of electrons can tell us where the Standard Model of physics is lacking. Some scientists have developed theories based on squished electrons and others on round, but the squished option has been seen as the much more interesting and potentially helpful of the two.
To test the various competing theories, scientists from a project called Advanced Cold Molecule Electron Electric Dipole Moment Search (ACME) went in search of a property called the electric dipole moment. Researchers have theorized the electric dipole moment could deform electrons, leaving a dent on one end and a bulge on the other because of interactions with undiscovered massive particles.
The ACME team used a beam of ultra-cold, thorium-oxide molecules to bombard a test chamber. More than 1 million molecules zipped through the apparatus 50 times per second. At the same time, researchers bounced lasers off the atoms and observed the reflections. A particular bend in the light would confirm the electric dipole moment, but they got nothing. At least for now, we have to conclude electrons are round.
The Standard Model predicts that electrons should be round — any warping from other particles would be so minor that we couldn’t detect it. This isn’t good news, though. We know the Standard Model is incomplete because it doesn’t explain things like dark matter. Identifying the errors in the model could help us develop a theory that does explain all the observable particles in the universe, as well as point the way to new ones.
The particles scientists have theorized affecting electrons may still exist, but their properties could be vastly different than anyone thought. It’s going to take more work to work out where the Standard Model diverges from reality.
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