HOWTO to generate electromagnetic background

This page contains some general descriptions of the generation procedures of electromagnetic background. There are several parameters which has to be set 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 to 1.1 or 11.0 corresponding to the  tagged photon beam intensities 
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 can be set using EBREMS_MIN card. 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 background photons is automatically scaled as follows:
     Rate(E_gamma > Thr)  =  Rate(E_gamma = 0.12 Gev) *k,
where k is a calibration coefficient. Note, Rate(E_gamma = 0.12 Gev) is set by the BGRATE parameter; 
it should correspond to 1.1 or 11 GHz of the  photon rates for high (10^7 photons/sec) and low 
(10^8 photons/sec) luminosities, respectively.