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Introduction

The detector simulation performs a Monte Carlo integration by tracking particles through the materials of our detectors and their surroundings until any are registered (hit) sensitive elements (PMTs, RPCs). The main package that provides this is called DetSim.

DetSim provides the following:

  • Glue Geant4 into Gaudi through GiGa
  • Takes initial kinematics from a generator, converts them to a format Geant4 understands.
  • Takes the resulting collection of hits and, optionally, any unobservable statistics or particle histories, and saves them to the event data store.
  • Modified (improved) Geant4 classes such as those enacting Cherenkov and scintillation processes.

The collection of “unobservable statistics” and “particle histories” is a fairly unique ability and is described more below.

Configuring DetSim

The DetSim package can be extensively configured. A default is set up done like:

import DetSim
detsim = DetSim.Configure()

You can provide various options to DetSim‘s Configure():

site
indicating which site’s geometry should be loaded. This can be “far” (the default) or one of the two near sites “dayabay” or “lingao” or you can combine them if you wish to load more than one.
physics_list
gives the list of modules of Physics processes to load. There are two lists provided by the configure class: physics_list_basic and physics_list_nuclear. By default, both are loaded.

You can also configure the particle Historian and the UnObserver (unobservable statistics collector). Here is a more full example:

import DetSim.configure
# only load basic physics
detsim = DetSim.configure(physics_list=DetSim.configure.physics_list_basic)
detsim.historian(trackSelection="...", vertexSelection="...")
detsim.unobserver(stats=[...])

Details of how to form trackSelection, vertexSelection and stats are given below.