SOLAr-sim

SOLAr-sim implements a Geant4-based Monte Carlo simulation of a generic LAr TPC for studying low-energy events in the context of the SOLAr project.

Disclaimer

This code has never been properly tested, but there are some reasonable expectations for it to work on a Linux machine. While offering my sincerest sympathies for your struggles, I cannot bear the responsibility for other developers' tears.

In the source code one may find large sections commented and ``peculiar'' choices for some names (such as Tank to indicate the cryostat). This is happening because a large part of this code is based on a MC simulation I developed for WbLS optical neutrino detector. Hopefully, a more appropriate naming convention will gain ground.

Prerequisites (on a Linux machine)

• Core: Geant4 v11.0 and newer, compiled without MULTI_THREAD support, ROOT (possibly compiled from source) and respective dependencies (cmake, g++, gcc)

• Generators: SOLAr-sim integrates some external events generators that are relevant for the physics goal of the project.

  • MARLEY: Low-energy neutrino interactions in LAr
  • BxDecay0: Generic radioactive decay generator, with the possibility of producing neutrinoless ββ-decay final states.

• Utilities: SOLAr-sim uses the RapidJSON package to parse configuration files formatted according to the json standard.

  At the preset state of the development, these three packages have to be installed manually by the user. The SOLAr-sim package includes a convenient script to automatically download, build and install the external dependencies (see External dependencies installation and configuration).

Download and build the project

The procedure to build the code have some subtle differences wether one is installing the simulation on a generic machine or on a more complex system such as the CERN computing environment.

Installing G4SOLAr on CERN lxplus

Step 1 - Download the project from github, setup the environment and install dependencies

$ git clone https://github.com/SoLAr-Neutrinos/SOLAr-sim.git

After cloning the repository, setup the needed dependencies that are already installed on the FNAL ecosystem by sourcing the setup_g4solar.sh script.

$ cd G4SOLAr
$ source setup_g4solar_lxplus.sh

If the project dependencies are not yet installed, follow the instructions on this page.

Step 2 - Build

Create a build and install directory, then build and install the project

$ mkdir build install && cd build 
$ cmake -DGeant4_DIR=${GEANT4_DIR} -DCLHEP_EXTERNAL=${CLHEP_INC} -DCMAKE_INSTALL_PREFIX=../install [opts...] ../G4SOLAr
$ make
$ make install

The project will search for the external dependencies in the G4SOLAR_EXT_DIR (by default set to G4SOLAr/extern/). You can specify a specific installation directory by setting it in the cmake command line (-DG4SOLAR_EXT_DIR=/my/g4solar_ext/path). Note that the geant4 version installed on dunegpvm nodes is compiled against an independent installation of CLHEP, so one has to specify the CLHEP include directory when calling cmake.

Installing SOLAr-sim on a generic machine

Step 1 - Download the project from github and install dependencies

$ git clone https://github.com/SoLAr-Neutrinos/SOLAr-sim.git

If the project dependencies are not yet installed, follow the instructions on this page.

Step 2 - Build

Create a build and install directory, then build and install the project

$ mkdir build install && cd build 
$ cmake -DGeant4_DIR=/path/to/geant4/install -DCMAKE_INSTALL_PREFIX=../install [opts...] ../G4SOLAr
$ make
$ make install

The project will search for the external dependencies in the G4SOLAR_EXT_DIR (by default set to G4SOLAr/extern/). You can specify a specific installation directory by setting it in the cmake command line (-DG4SOLAR_EXT_DIR=/my/g4solar_ext/path).

Run SOLAr-sim

It is possible to run the simulation directly from the installation folder, but it is advised to add the build directory to the executable PATH to be able to run the simulation more flexibly on your machine

$ cd install
$ export PATH=${PWD}:${PATH}

The solar_sim executable can take the following inputs:

solar_sim      [-m/--macro macro_file]            #<< Geant4 mac file
               [-r/--seed user_seed]              #<< User defined seed
               [-g/--geometry geometry_cfg_file]  #<< Geometry description
               [-p/--materials material_db_file]  #<< Material definition table
               [-h/--help print usage]

The first input (-m, --macro) is the configuration file for the Geant4 run. There one can specify the type of generated events, their number, the output file, etc. A collection of examples can be found in the macros/ folder. The commands defined in the messenger classes are briefly commented in the macro files.

The second input (-s, --seed) is the random engine seed provided by the user.

The third input (-g, --geometry) is the json configuration file describing the dimensions of the detector and of all the sub-systemd.

Finally, the fourth input (-p, --materials) is a json table containing the definitions of all materials used in the simulation.

If no geometry or material table are provided, the simulation will take by default assets/geometry/geometry.json and assets/materials/materials_db.json respectively.

Interpreting the output

The output file consists in a ROOT Tree containing the full development of an event at the step-level and the information from the photon detection system. These two distinct set of informations are stored into a SLArMCEvent object, which in turn contains a vector of SLArMCPrimaryInfo (one for each particle in the initial state) and the PDS event object (SLArEventReadoutTileSystem).

Primary info

In addition to its own trajectory, each "primary" carries the trajectories of all secondary particles associated with the primary track. The points of each trajectory are defined by their spatial coordinates and by the energy deposited in the step.

The "hierarchical" structure of the primary information object is represented in the figure below (Fig. 1)

Fig. 1 Box diagram showing the structure of a SLArMCPrimaryInfo object

Photon Detection System Info

The photon hits recorded by the photon detection system are recorded in a dedicated event object. In the case of readout tiles, with each tile mounting up to 100 SiPM, the detected photons are grouped together in a single score.

TODO: add to the photon hit attributes the identification of the specific SiPM responsible for the detection.

Figure 2 schematically represents the structure of the ReadoutTile-based PDS event object.

Fig. 2 Schematic representation of the event class for the PDS based on the readout tile concept

SOLAr Event Dictionaries

To be able to access the event information in an interactive ROOT session, one should load the shared libraries defining the event and configuration objects. These libraries are built when compiling SOLAr-sim and are installed in the G4SOLAR_INSTALL_DIR/lib folder. During the installation process, a rootlogon.C file loading the libraries is created in G4SOLAR_BASE_DIR/SOLArAnalysis. In the same folder, one can find the script test_output.C, which can serve as an example for accessing simulated MC event.

Running jobs on the grid

CERN

Work in progress

FNAL

You can run SOLAr-sim jobs on the grid with

cd grid
source setup_g4solar_grid.sh
python jobsub.py [options]

You can see all the available options with python jobsub.py -h

jobsub.py uses a template macro to run the jobs. The current available template is template_g4solar_electrons.mac. To run other types of events, more templates will have to be added.

TODO: add a full macro file writer