BEXCO - Room F(201/202/203/204)
[GA002] A Bethe-Heitler 5D polarized photon-to-e+e-pair conversion event generator
Current pair conversion event generators (e.g. geant4 and EGS5 physics models) don't sample the five-dimensional differential cross section (5D DCS), but instead a product of 1D DCSs. In addition, most of them use high-energy and/or small angle approximations. Also the electron and positron polar angles are often generated independently so that energy-momentum is not conserved. Few of them can simulate the conversion of linearly polarized photons, and only at high energy [arXiv:1612.06239, to appear in Astropart. Phys.]. I have written an event generator that is sampling exactly the 5D Bethe-Heitler DCS, including for photons with a non-zero linear polarization fraction [NIM A 729 (2013) 765]. This event generator is using the BASES/SPRING instantiation of the VEGAS method : at a given energy, for a given target nucleus (nuclear conversion) or atom (triplet conversion), after a 5D grid has been optimized for DCS integration precision that is for event generator efficiency, the DCS is tabulated and stored, something that needs several seconds of computation. Then zillions of gamma conversions can be generated quickly at that energy and for that target. The polarization asymmetry properties of the Bethe-Heitler DCS were examined with that tool in Astropart. Phys. 88 (2017) 30, especially at low energy where most of the statistics is for cosmic sources. I am now developing a VEGAS-free version of that code, that will allow the fast generation of the conversion of a photon of a given energy on a given target, with the same other properties as for the VEGAS-based generator, i.e., 5D, exact, polarized and strictly energy-momentum conserving.