We have large angle pair production data from 5.5 GeV brems photons, where pairs are detected at more than 20 mrad, and we are comparing data and simulation. In pair production, four variables, typically Energy(e+), Theta(e+), Theta(e-), and Phi, are necessary to specify the final state. Since it is not trivial to sample from a four-variable function and photoproduction takes place at a very small angle, various approximations are used. Both EGS5 and Geant4 assume Phi=180 deg. Geant4 assumes Theta(e+)=Theta(e-), while EGS5 treats Theta(e+) and Theta(e-) independently. Both EGS5 and Geant4 assume no correlation between Energy and angle. The double rate, where both e+ and e- are scattered more than 20 mrad, is very sensitive to the approximation used in simulation. Fluka seems to yield best agreement with data. I am looking for the function that Fluka uses to simulate pair production, and any approximations used. I cannot find Physics Reference Manual in Fluka web site.
Takashi Maruyama
SLAC
Received on Tue Jul 09 2013 - 09:30:05 CEST
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