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randa177
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why is the cross section of photon - proton less than the electron- photon cross section for the same photon energy??
Because the photon does not carry electric charge ?randa177 said:why is the cross section of photon - proton less than the electron- photon cross section for the same photon energy??
Well, the proton carries electric charge, and the electron carries electric charge as well, so they interact by exchanging a virtual photon (say for instance in the lowest order appriximation). I guess you are asking about a real photon. How a real photon interacts with a proton depends on the energy of course. At energies around the proton mass and/or QCD scale (which I guess is your question, since ultra-high energy photons can not be produced easily) you can effectively describe the proton-photon interaction by the photon hadronic content, which fluctuates say in a vector meson (or such hadronic configuration with the right quantum numbers). This is Regge calculus. So you need you photon to fluctuate into something else before interaction. You expect that this is going to considerably reduce your cross section.randa177 said:I don't understand how is that answer related to my question??
humanino said:Well, the proton carries electric charge, and the electron carries electric charge as well, so they interact by exchanging a virtual photon (say for instance in the lowest order appriximation). I guess you are asking about a real photon. How a real photon interacts with a proton depends on the energy of course. At energies around the proton mass and/or QCD scale (which I guess is your question, since ultra-high energy photons can not be produced easily) you can effectively describe the proton-photon interaction by the photon hadronic content, which fluctuates say in a vector meson (or such hadronic configuration with the right quantum numbers). This is Regge calculus. So you need you photon to fluctuate into something else before interaction. You expect that this is going to considerably reduce your cross section.
The cross section of a particle interaction is a measure of the probability of that interaction occurring. In the case of photon-proton interactions, the cross section refers to the likelihood of a photon colliding with a proton and producing a new particle or changing the trajectory of the proton. On the other hand, electron-photon interactions refer to the probability of an electron interacting with a photon and producing a new particle or changing the trajectory of the photon.
The cross section of photon-proton interactions is typically larger than that of electron-photon interactions. This is because protons have a larger mass compared to electrons, making them more likely to interact with photons. Additionally, protons are composed of smaller particles called quarks, which increases the chances of interactions with photons.
Several factors can affect the cross section of these interactions. One of the main factors is the energy of the particles involved. Higher energy particles have a larger cross section due to their increased likelihood of interacting with each other. The type and properties of the particles also play a role, as well as the angle at which the particles collide.
The cross section of photon-proton interactions is typically measured using particle accelerators. By colliding photons and protons at different energies and angles, scientists can study the resulting particles and calculate the cross section. These measurements can also be compared to theoretical predictions from particle physics models.
Understanding the cross section of these interactions can provide valuable insights into the fundamental properties of particles and the laws of physics. It also has practical applications, such as in the development of medical imaging technologies and in studying the behavior of particles in high-energy environments, like in the early universe or in particle accelerators.