Astronomy and Astrophysics – Astrophysics
Scientific paper
Apr 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002aps..apri10007a&link_type=abstract
American Physical Society, April Meeting, Jointly Sponsored with the High Energy Astrophysics Division (HEAD) of the American As
Astronomy and Astrophysics
Astrophysics
Scientific paper
Exclusive pion electroproduction is one of the major tools for accessing the properties of excited nucleon states. New experiments with polarized electrons at CLAS in Jefferson Lab provide high precision and wide kinematic coverage, including angular distributions and out-of-plane measurements. It allows one to obtain information about all five coincidence structure functions in the reactions <~belprocess e + p &-> & e' + π^+ + n, e + p &-> & e' + π^0 + p . In order to interprete the data, one needs to include the effect of electromagnetic radiative corrections (RC) into the analysis. Detection of a final-state hadron in addition to the electron requires development of new algorithms for computing RC. We developed such algorithms in application to exclusive electroproduction of pions. Our approach is based on the Bardin-Shumeiko method of covariant extraction of infrared divergence. The hadronic tensor was treated in a covariant way and it required models in order to perform the numerical analysis. A FORTRAN computer code EXCLURAD was written using the exact and leading log formulae to compute RC for the unpolarized cross section and beam spin asymmetry of exclusive pion electroproduction. Three models were used for the electroproduction structure functions: a) MAID98 and MAID2000, b) the model developed by Sato and Lee, and c) AO model. The calculation can be done with or without a cut on inelasticity. Numerical analysis carried out for the kinematic conditions at Jefferson Lab allows us to make the following conclusions. RC to the cross section is very sensitive to the cut on inelasticity. Using a harder cut leads to smaller corrections. A hard cut can also suppress corrections to the beam spin asymmetry. The correction to cross section can be tens of per cent. A model dependence of the correction has been studied. The correction has a non-trivial angular dependence in \cos θ and φ. This angular dependence of RC is important in performing the partial wave analysis and determination of the parameters for electroexcitation of nucleon resonances.
Afanasev Andrei
Akushevich Igor
Burkert Volker
Joo Kyungseon
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