Nuclear shadowing effect I am reading some texts which mention the nuclear shadowing effect (NSE). However, they don't explain explicitly what is NSE. So my questions are as follows:


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*What is the NSE?

*What is its origin?
 A: The expression of cross section for lepton-nucleon collision has term specifying the finite extent of charge distribution of nucleon. 
When expressed in terms of lorentz invariant kinematic variables like x and $Q^2$, this term is referred to as 'Structure Function, $F_2$'. This is an experimentally measurable quantity. We measure it for nucleon as well as nuclei collision with lepton (say, electron).
We have a very good model to find various parameters(e.g. cross section, number of participating nucleons etc) of nucleus-nucleus(AA) collision called as Glauber Model.
The basic assumption of this model is that AA collisions could be build up from nucleon-nucleon(pp) collisions. If this is to be true, we expect that
$Nuclear\; Ratio, R= \frac{{F_2}^{nuclei}/A}{{F_2}^{nucleon}}=1 $
where A is mass number of nuclei and ${F_2}^{nuclei}$ and ${F_2}^{nucleon}$ are experimentally measured values of structure functions of nuclei and nucleons respectively.
But we find out that Nuclear Ratio, R is not 1, but varies with x for a constant $Q^2$ as follows

For low x values, it implies that we get lower lepton-nuclei collision cross section than what we would have expected from scaled up lepton-nucleon collision cross section.
This is as if, the central nucleons of nuclei are being shielded due to surface nucleons. This is called Shadowing Effect.
Shadowing is caused by 'multiple scattering' of quark pair produced from the virtual photon emitted by the lepton. I do not understand this part well.
There are various models to explain shadowing:


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*Vector meson dominance

*Parton recombination

*Glauber-like rescattering

*Gribov inelastic shadowing


References:


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*Modern Particle Physics by Mark Thompson, Chapter on Deep inelastic Scattering (DIS)

*Nuclear Shadowing

*Nuclear Shadowing in a Parton Recombination Model by S. Kumano

*Glauber Model
