Collision of photon and proton

[sanpokhrel]

In what condition does a photon hit a proton? What happens to the energy of the photon in that case? Does proton emit another photon and goes down to the initial energy state?

 

[NFuller]

At low energies $<1$MeV, the photon will simply scatter off of the proton in a process called Compton scattering. See here https://en.wikipedia.org/wiki/Compton_scattering. At higher energies where the photon energy becomes similar to the proton binding energy, the photon may cause the proton to decay. There is also the issue of pair production which occurs at higher energies and will affect the scattering process. I'm not an expert in high energy physics so I can't really describe the details of what happens in these extreme scenarios. The low energy regime however is pretty easy to understand.

 

[Gigaz]

Scattering of photons on protons happens all the time and for all kinds of photons. However, the scattering rates are generally dominated by the contributions from the electrons. The mass of the nucleus is comparably large so that it doesn't follow the photons electric field as easily as the electrons. There are some resonance energies though where proton-photon interactions are be important.

 

[Nugatory]

In general if something has an electric charge, or is a neutral composite of charged particles, it will interact with electromagnetic fields. In a complete quantum-mechanical analysis of these situations, those interactions will be represented as "collisions with photons".

(The quotes are there because the phrase works better for a B-level informal description than for a serious presentation).

 

[tom.stoer]

At all energies there is elastic scattering.
At specific resonance energies one finds excited states, e.g. the Delta resonances of proton and neutron.
From specific threshold energies upward scattering channels for pair production open, e.g. the electron-positron pair production, pion-pair production etc.