Both electrons and photons are defined in the SM as point-like particles. The electron does have rest mass while the photon is massless.
Now if I search for the upper limit on the size of the electron, I find a lot of questions, experiments, and even the official Particle Data Group list the upper limit on the electron radius (page 109).
The only official looking paper I have found on photon radius is this:
So far so good. Now if I try to search for the upper limit on the radius of the photon, I find a big empty nothing (official at least, and we do not rely on popsci articles). Experiments are usually for the photon mass (but not the radius). Why is that? Is it just the rest mass? Or is there another fundamental difference (EM charge maybe) that somehow makes a experiment able to be performed for the electron radius but not the photon radius? Most of the experiments and calculations for electrons talk about form factors, are these available for electrons only and not photons?
- Why is there no official word on the upper limit of the photon radius (while there is for the radius of the electron)?