Theoretically electron is a point particle but in reality it has an effective size due to flickering quantum fields around it.

If electron has an effective size what is the shape of it. Is it round? Is it elongated? Physicists have been measuring (establishing upper bounds) for a quantity known as the electron’s electric dipole moment to answer this question.

If the electron electric dipole moment is zero then it means that electron’s effective shape is perfectly round.

On the other hand, if the electron electric dipole moment is nonzero then it means that we need a better theory than the “Standard Model” of elementary particles.

There is a new experimental result https://arxiv.org/abs/2212.11841

The new upper bound for electron electric dipole moment =

which is very close to zero. Electron effective shape seems to be perfectly round.

Quanta Magazine does a better job explaining this story:

The Electron Is So Round That It’s Ruling Out Potential New Particles

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