CLAS12 Forward Time-of-Flight Example

This example shows the CLAS12 Forward Time-of-Flight (FTOF) geometry from clas12-systems. It is upcoming in the next release.

Quickstart

From the clas12-systems repository, build the geometry database and run a short simulation:

cd $GEMC_HOME/../clas12-systems/geometry_src/ftof
./ftof.py
gemc ftof.yaml -n=1

Geometry

The geometry, shown below, is defined in geometry_src/ftof/ftof.py and geometry_src/ftof/geometry.py. The FTOF builder reads the local coatjava geometry factory, converts the CLAS12 forward TOF panels and scintillator paddles to GEMC volumes, and stores them in gemc.db.

The world (a box named root) contains, for each of the six sectors:

three panel mother volumes named ftof_p1a_s<sector>, ftof_p1b_s<sector>, and ftof_p2_s<sector>
scintillator paddles named panel1a_sector<sector>paddle<n> (23 paddles), panel1b_… (62), and panel2_… (5)
a lead shield behind panels 1a and 2 named ftof_shield_p1a_sector<sector> and ftof_shield_p2_sector<sector>

Interactive viewer:

Physics List

FTFP_BERT is used by default, selected in the YAML file with phys_list: FTFP_BERT.

phys_list

The physics list can be selected using the option
gemc -phys_list <value>
where <value> can be a combination of the Geant4 physics constructors separated by the + sign. For example
gemc -phys_list="FTFP_BERT + G4NeutronCrossSectionXS"
To see a list of the available Geant4 constructors:
gemc -showPhysics

Generator

The particle kinematics are defined in the YAML file:

gparticle:
  - name: e-
    p: 5000*MeV
    delta_p: 1*GeV
    theta: 25*deg
    delta_theta: 12*deg
    randomThetaModel: cosine
    delta_phi: 180*deg

See also the Internal Generator Documentation for more information.

Digitization

The scintillator paddles use the CLAS12-specific ftof digitization plugin. Each paddle is read out at both ends, so the plugin splits every hit into a Left and a Right PMT channel. The identifiers record sector, panel, paddle, and PMT side:

gvolume.digitization = "ftof"
gvolume.set_identifier("sector", sector, "panel", layer, "paddle", paddle, "side", 0)

Usage

Building the detector

Use geometry_src/ftof/ftof.py to build the detector. By default, the setup is stored in a SQLite file named gemc.db.

See also the Building Geometry for more information.

Running GEMC

The file ftof.yaml can be used to run the setup. Add -gui to run interactively:

gemc ftof.yaml -gui

Modify ftof.yaml as needed, in particular to add particles, control the number of threads, or change the output.

Running Events

CLAS12 FTOF simulation: generated electrons crossing the forward time-of-flight geometry.

Output

The gstreamer option selects the output filenames and formats:

gstreamer:
  - format: csv
    filename: ftof
  - format: hipo
    filename: ftof

See also the Output Documentation for more information.

Plotting with the GEMC Analyzer

Run GEMC with 2,000 events first. The default YAML file writes the analyzer CSV streams.

gemc ftof.yaml -n=2000 -no_field=all -plugin_path=/opt/projects/gemc/clas12-systems/build

Plot the total energy deposited per hit:

gemc-analyzer ftof_t0_true_info.csv totalEDeposited --kind csv --data true_info

FTOF total energy deposited per hit

Plot the y vs x hit positions:

gemc-analyzer ftof_t0_true_info.csv --kind csv --data true_info --plot yvsx --bins 80

FTOF y vs x hit positions