Primakoff photoproduction of eta off Helium4

Version I

The simulation can be found here: /cache/halld/gluex_simulations/PrimEx-eta-phase-I/eta-he4-19062021

There are in fact 4 distinct simulations

• Primakoff only (Geant4_bkg_None_runnb_?????_gen_primex_eta_he4_to_2g_rim)
• Primakoff + Coherent + interference (Geant4_bkg_None_runnb_?????_gen_primex_eta_he4_to_2g)
• Quasi-free off proton (Geant4_bkg_None_runnb_?????_gen_primex_eta_he4_to_2g_inc) and neutron (Geant4_bkg_None_runnb_?????_gen_primex_eta_he4_to_2g_inc_n)

For each set, 20M events were thrown between 6 and 12GeV corresponding to the He (full target) runs range ie 323 runs. The number of events simulated for each run is proportional to the flux of this wrt to the total 323 runs flux.