Difference between revisions of "HOWTO to generate electromagnetic background"

Revision as of 18:13, 14 May 2008

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.

Fig. 1. Scale factor for the EM background rate as function of the energy threshold of generated Bremsstrahlung photons. The scale factor equals to 1 at E_gamma = 0.12 GeV

Examples

To study detector responses for electromagnetic background the following MC samples can be used:

1. MC sample containing a single photon per event.

Note, the photon is NOT required to pass throught the collimator into a 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). The following parameters has to be set in the control.in file

• BEAM 12. 9.

Optional

• EBREMS_MIN THR

THR is a threshold on the min Bremsstrahlung photon energy. The default value is 0.12 GeV.

1. Pile-up of electromagnetic background. MC sample with electromagnetic interactions superimposed

in a specific time interval. The time interval might correspond to the trigger or readout integration gates