I'm writing a piece about the electron, and I'm having trouble finding evidence to back up the claim that the evidence is pointlike.
People tend to say the observation of a single electron in a Penning trap shows the upper limit of the particle's radius to be 10-22 meters. But when you look at Hans Demelt’s Nobel lecture you read about an extrapolation from the measured g value, which relies upon "a plausible relation given by Brodsky and Drell (1980) for the simplest composite theoretical model of the electron". This extroplation yields an electron radius of R ≈ 10-20 cm, but it isn't a measurement. Especially when "the electron forms a 1 μm long wave packet, 30 nm in diameter".
It's similar when you look at The anomalous magnetic moment and limits on fermion substructure by Brodsky and Drell. You can read things like this: "If the electron or muon is in fact a composite system, it is very different from the familiar picture of a bound state formed of elementary constituents since it must be simultaneously light in mass and small in spatial extension". The conclusion effectively says if an electron is composite it must be small. But there's no actual evidence for a pointlike electron.
Can anybody point me at some evidence that the electron is pointlike?