HOWTO to generate electromagnetic background
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This page contains some general descriptions of the generation procedures of electromagnetic background. There are several parameters which has to be set up in the control.in to handle the simulation:
- BEAM 12. 9.
Electron beam energy and position of the coherent Bremsstrahlung peak.
- BGRATE 11.0
The rate of background photons in GHz (in the Tagger region before the collimator). This parameter should be set either to 1.1 or 11.0 which would correspond to intensities of the tagged photon beam of 10^7 and 10^8 photons/sec on target, respectively. For high-luminosity runs one should use 11.0.
- BGGATE -50. 50.
Time interval in the ns, the earliest and the latest time, where the background photons are produced. This parameters is used to simulate electromagnetic pile-up events.
- EBREMS_MIN 0.12
The low energy of generated Bremsstrahlung photons. If EBREMS_MIN is commented, or set to 0, the default photon-energy threshold of 0.12 GeV is used. If EBREM_MIN is set, the rate of generated background photons is automatically scaled as follows: Rate(E_gamma > Thr) = Rate(E_gamma = 0.12 Gev) *K( E_gamma = Thr), where K is a calibration coefficient which depends on the photon energy threshold, Thr. The dependence of K on the energy threshold is shown in Fig. 1. Note, Rate(E_gamma = 0.12 Gev) is set by the BGRATE parameter as has been explained in the previous paragraph.
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To study detector responses for electromagnetic background the following MC samples can be used:
- MC sample containing one generated photon per event.
Note, the photon is NOT required to pass throught the collimator into the detector area, i.e., in most cases it will get stuck in the collimator volumes (the number of photons which pass throught the collimator is, on average, about a factor of seven less than that produced for the entire energy spectrum)