Dilepton production in NN collisions

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Dilepton production in NN collisions
A comparison of
Shyam Mosel Phys. Rev. C. 67, 065202 (2003)
and
Kaptari Kaempfer Nucl. Phys. A 764, 338 (2006)
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Both include contribution from the following
diagrams
Intermediate mesons ?, ?, s, ? Box ? isobar
or nucleon intermediate states
Lagrangians, coupling constants, form factors,
cut off parameters are the same in two
calculations
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Differences in two calculations
Gauge Invariance when using the electromagnetic
form factors for half off shell photon production
vertices
Nucleon-nucleon-photon vertices
Not independent WT
?
LNN? -e?GNN?? A?
?




GNN? -ieSF1 ?? F2 (is??k?/2mN ) F3 k? ?
Use on-shell form of the vertex also for the
off-shell momenta
F1 F1- F1, F2 F2- F2, F3 F3- F3 0
Multiply the external photon emission vertices by
the same form factors that multiply the hadronic
vertices.
Multiply the internal photon production diagrams
by an additional factor
Fint 1 (m2meson q21 )/(?2-q22) (m2meson
q22 )/(?2-q21)
Hagalin, Kapusta, Gale, Phys. Lett. B 224, 433
(1989), Towner, Phys. Rep. 155, 263
(1987) Feuster and Mosel, Phys. Rev. C 58, 457
(1998)
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Comparison with Kaptari and Kaempfer
Bremsstrahlung of KK is larger by factors of 2-3
Delta is also larger by factors of 2
Total is larger by the similar factor
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A possible way to solve this problem
Compare with the DLS data
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