Spherical electric field of electron.

[skybobster]

On May 25, 2011, the journal Nature published an article stating that the electron was experimentally found to be extremely spherical. In Volume II, Chapter 5 of Feynman's Lectures on Physics, he states that the electric field of an electron has been experimentally determined to vary significantly from 1/r^2 as one approaches the center, where the field is singular. He gives no reference for this remark. Does anyone know of experimental results which have determined the electric field (or potential) as a function of the radial distance r for an electron (assuming spherical symmetry as a first approximation)?

 

[Bill_K]

The experiment you mention is very important, and it's unfortunate that the popular accounts of it make it sound so trivial, that the electron is "very round."

What they did was to attempt to measure the electron's electric dipole moment. A nonzero electric dipole moment would violate CP invariance. In the standard model, the electron does have an electric dipole moment but it is extremely small, about 10^-42 e-cm. Most alternative models including supersymmetry and technicolor predict a much larger moment, around 10^-29 e-cm.

The present experiment failed to find a moment but pushed the limit down to 10^-28 e-cm, almost to the point where some of the leading theories would be eliminated.

 

[RedX]

Is the electron's electric dipole moment aligned with its spin direction (like the magnetic moment)?

If not, then to fundamentally specify an electron, do you have to specify its momentum, electric dipole moment direction, and spin, respectively:

$$\psi=\psi_+(p,\theta_{e-d},\phi_{e-d})|+>+\psi_-(p,\theta_{e-d},\phi_{e-d})|->$$
Also, can an electron have quadrapole moments? Isn't there a limit to the number of possible form factors (since there are a finite combination of gamma matrices), so eventually the electron can't keep on having new features such as extra moments?