Experimental boundaries for size of electron?
Posted: Sat Aug 25, 2018 10:10 pm
There is some confidence that fundamental particles are perfect points e.g. to simplify QFT calculations - what experimental evidence do we have, especially for electron?
Electron Wikipedia article only points argument based on g-factor being close to 2:Dehmelt's 1988 paper extrapolating (by fitting parabola to two points!) from proton and triton behavior that RMS (root mean square) radius for particles composed of 3 fermions should be ≈ g−2:
Another argument for point nature of electron might be tiny cross-section, so let's look at it for electron-positron collisions for GeV scale:
As we are are interested in size of resting electron (no Lorentz contraction), we should extrapolate the flat line sigma ~ 1/E^2 to resting electron, getting sigma ~ 100mb corresponding to ~2fm radius.
From the other side we know that two EM photons having 2 x 511keV energy can create electron-positron pair, hence energy conservation doesn't allow electric field of electron to exceed 511keV energy, what requires some its deformation in femtometer scale from E ~ 1/r^2:
Can we bound size of electron from above: g-factor or scattering experiments?
Is there other experimental evidence?
Electron Wikipedia article only points argument based on g-factor being close to 2:Dehmelt's 1988 paper extrapolating (by fitting parabola to two points!) from proton and triton behavior that RMS (root mean square) radius for particles composed of 3 fermions should be ≈ g−2:
Another argument for point nature of electron might be tiny cross-section, so let's look at it for electron-positron collisions for GeV scale:
As we are are interested in size of resting electron (no Lorentz contraction), we should extrapolate the flat line sigma ~ 1/E^2 to resting electron, getting sigma ~ 100mb corresponding to ~2fm radius.
From the other side we know that two EM photons having 2 x 511keV energy can create electron-positron pair, hence energy conservation doesn't allow electric field of electron to exceed 511keV energy, what requires some its deformation in femtometer scale from E ~ 1/r^2:
Can we bound size of electron from above: g-factor or scattering experiments?
Is there other experimental evidence?