Re: What is a photon

William Hyde <wthyde1953@gmail.com> wrote or quoted:

Still, I've been unable to find any observations of free protons
becoming neutrons + anti-neutrino on collision with a fast electron.

  Looks like turning a proton into a neutron by grabbing an electron
  happens in nuclei, but not with free protons. I couldn't really
  figure out why. Maybe it's just tough for free protons to keep both
  energy and momentum in check at the same time. But apparently, there
  have been some experiments where protons and electrons collide.
  At least I found one quote from a source that seems reliable:

|In electron-proton scattering the proton structure is probed
|by a photon probe emitted from the electron side. If also the
|proton emits a photon, the domain of two-photon physics is
|entered, which has been analysed in detail at e+ e− colliders.
|At electron-proton machines photon-photon scattering is the
|dominant production process for muon pairs at high energetic
|scales.

  At least this brings us back to the "photon" from the subject.