Simulation Software
From GlueXWiki
Simulated data is most often used to determine the detector efficiency (acceptance), so that the yield of measured data can be adjusted to compensate for uneven detector efficiency (eg when tracks are not detected because they enter the gaps between the drift chambers or the calorimeters).
There are several steps in the production of simulated data.
- Event generators (bggen, gen_amp, etc) produce a set of events as a list of particle track properties - mass, momentum and angle. The distribution of the events is determined in the generator. Bggen produces typical hadronic background events, whereas the other generators mimic specific reactions, with mass and angular distributions described by the user. Within those distributions, random numbers are used to determine the momentum of the primary particle and the momenta of its decay products. This randomness is why the process is often called a Monte Carlo (referring to casinos).
- HDGeant4 uses a model of the materials making up each part of the GlueX detector to find out what would happen to the simulated tracks as they pass through the detector. It uses Geant4 to model track scattering and energy loss, and produces a list of the time, position and energy deposition of hits that would be measured.
- The particle gun is a part of HDGeant4 that can be used instead of the event generators to specify the particle, momentum and track angles. This can be useful to investigate detector efficiency features.
- Mcsmear models the resolution of the detector, and adjusts the time, position and energy of the hit quantities so that the output data become less exact and look like a genuine measurement using the GlueX detector.
- 'Random trigger' events are collected during experimental runs, using a separate trigger which is generated at regular time intervals (from a pulser). This records the hits that are in the detector at that time. These can be added to the simulated data to mimic the 'noise' hits from extra tracks through the detector which were not associated with hadronic production events.
