simulation

TRD simulation cheat-sheet

Using configurable params to pass additional options to the generator for generating specific events

• Generate events with an electron particle gun in |eta| < 0.84:

  o2-sim -m PIPE MAG TRD -n 1000 -g boxgen --configKeyValues 'BoxGun.pdg=11;BoxGun.eta[0]=-0.84;BoxGun.eta[1]=0.84'

• Generate events with an electron particle gun with 0.5 < p < 2.5 GeV and |eta| < 0.84:

  o2-sim -m PIPE MAG TRD -n 1000 -g boxgen --configKeyValues 'BoxGun.pdg=11;BoxGun.eta[0]=-0.84;BoxGun.eta[1]=0.84;BoxGun.prange[0]=0.5;BoxGun.prange[1]=2.5'

• Generate events with a pion particle gun in |eta| < 0.84:

  o2-sim -m PIPE MAG TRD -n 1000 -g boxgen --configKeyValues 'BoxGun.pdg=211;BoxGun.eta[0]=-0.84;BoxGun.eta[1]=0.84'

• Generate events with a pion particle gun with p = 2 GeV and |eta| < 0.84:

  o2-sim -m PIPE MAG TRD -n 1000 -g boxgen --configKeyValues 'BoxGun.pdg=211;BoxGun.eta[0]=-0.84;BoxGun.eta[1]=0.84;BoxGun.prange[0]=2;BoxGun.prange[1]=2'

  Using TRD specific configurable params

--configKeyValues 'TRDSimParams.doTR=false;TRDSimParams.maxMCStepSize=0.1'

Generate Raw data from MonteCarlo:

o2-trd-trap2raw

This will convert the tracklets and digits in the current directory to a series of files containing the raw data as it would appear coming out of the cru. There are multiple options :

• -d [ –input-file-digits ] default of trddigits.root input Trapsim digits file, empty string to have no digits.
• -t [ –input-file-tracklets ] default of trdtracklets.root input Trapsim tracklets file
• -l [ –file-per ] how to distrbute the data into raw files.
  • all : 1 raw file
  • halfcru : 1 file per cru end point, so 2 files per cru.
  • cru : one file per cru
  • sm: one file per supermodule
• -o [ –output-dir ] output directory for raw data defaults to local directory
• -x [ –trackletHCHeader ] include tracklet half chamber header (for run3, and not in run2)
• -e [ –no-empty-hbf ] do not create empty HBF pages (except for HBF starting TF)
• -r [ –rdh-version ] rdh version in use default of 6
• –configKeyValues arg comma-separated configKeyValues

default would then be the following :

o2-trd-trap2raw -d trddigits.root -t trdtracklets.root -l halfcru -o ./ -x -r 6 -e

Some technical details:

Pileup implementation

There are two general cases: Case 1: The first signal triggers the readout at t=A. The signal is read out for 30 time bins (3 microseconds). A second signal can arrive at t=C. The second signal will contribute to the tail of the first signal with (B-C)*samplingRate bins from its head.

A        B
**********
      **********
      C        D

Case 2: A trigger happened in the past at t<A, but A is within the deadtime of the TRD so the detector can't trigger again and the signal isn't readout. Still, the signal can contribute to a future signal. When a new signal arrives at t=C that can trigger, the signal will be readout for 30 time bins and will have (B-C)*samplingRate bins from the tail of the previous signal onto it's head.

A        B
**********
      **********
      C        D

We keep a deque of signals that is flushed when the detector gets a new trigger. All signals are stored in the deque and are pop from the front only when they are too old. A signal can contribute to two events, one in the past and one in the future. See for example Case 3:

A        B
**********
        **********
        C        D
               **********
               E        F

In this example, we consider a trigger at t=A. The second signal contributes with (B-C)*samplingRate bins from its head onto the tail of the first signal. A third signal arrives at t=E, with E>A+BUSY_TIME, which can trigger the detector and be readout. The third signal will have (D-E)*samplingRate from the tail of the second signal onto its head. So, the requirement for a signal to be too old, and be dropped, is:

• new trigger arrives, and
• the time difference between the first time bin of the previous signal and the new trigger is greater than TRDSimParams.readoutTimeNS.