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Radiative Corrections

In double spin asymmetry analysis the electron nucleon scattering process is given as an one photon exchange event, so called the Born approximation(Fig 2.19). In reality, there are multiple photon effects during the experiments. These high order processes, also called radiative effects, can be calculated and used to correct the cross section data.

Figure 2.19. The Born Approximation

There are two types of radiative corrections, internal and external. Internal radiative corrections describe the contributions, which took place during the lepton-hadron interaction. In first order approximation they include vertex photon exchange, self energy and vacuum polarization Fig. 2.20.<ref name="RadiativeCorrections"> Nucleon Form Factors. In Scholarpedia, from http://www.scholarpedia.org/article/Nucleon_Form_factors#History </ref>

Vertex Photon Exchange	Vacuum Polarization
Self Energy	Self Energy

Figure 2.20 Internal Radiation

On the other hand, the external radiative corrections account for the Bremsstrahlung by the incoming and scattered electron and by the recoiling target nucleon Fig. 2.21.

Figure 2.21 Externall Radiation

One of the major advantages of the double polarization experiments is the minimum contribution from the radiative corrections. For the [math]~4.2 GeV[/math] incident electron beam data the radiative corrections are less than 5%<ref>http://www.jlab.org/Hall-B/secure/eg1/EG2000/fersch/QUALITY_CHECKS/file_quality/runinfo.txt</ref>. Due to negligible contributions from the radiative corrections, they are not included in the double spin asymmetry analysis.

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