Systems

A detector in gemc is composed by one or more systems, each a hierarchical collection of geant4 volumes. In the example below an example with two systems, Forward Detector and Central Detector, is shown.

Systems Hierarchy Visualisation	Corresponding Hierarchy List
	Forward detector paddles paddle 1 ... pmts pmt 1 ... Central detector shield paddles light guides lg 1 ... pmts pmt 1 ...

Create a system

To create a new system, use the sci-g template script scigTemplate.py. It setups a new directory with the name of the system containing template files with default geometry and materials.

For example, to create a ‘forward’ system:

scigTemplate.py -s forward

In the directory forward, the following files appear:

• README.md: a template markdown file
• forward.py: the main python script that calls geometry and material builders
• geometry.py: the geometry builder; has a box and a tube as example volumes
• materials.py: the materials’ builder; shows two different ways to define materials
• forward.jcard: the steering card that loads the detector and defines the event generator, the output and the options

Build the system and run gemc

Following the above example, to build the detector, execute forward.py. This will create the databases for the geometry and materials. The default database format is text and the default variation is default, so the files forward__geometry_default.txt and forward__materials_default.txt will appear.

To load the system in gemc, the following entry is added to the steering card:

"+gsystem": [
        {
          "system":   "./forward",
          "factory": "text",
          "variation": "default"
        }
]

The steering card also setups 200 events, each with one π⁰, with two outputs: a root file and a text file. Modify as needed and run gemc:

gemc forward.jcard

These steps have been summarized in the following recording:

Variations

The scigTemplate script accepts a -v option to create one or more variations of a system.
For example, to create a forward system with two variations, default and lead_target:

scigTemplate.py -s forward -v default lead_target

This will allow to have two versions of the same forward detector. As an example, the lead_target variation could be identical to the default except for the target material. For more details check the Variations Example.

## Database factories