FPFSim

Geant4-based simulation package for detectors in the Forward Physics Facility.

Setting up on lxplus

The LXPLUS service at CERN (lxplus.cern.ch) provides a cluster of machines for interactive computing as well as access to the HTCondor batch system for job submission. Provided you have a valid CERN computing account, you can access LXPLUS following these instructions:

1. Visit the list of services at the CERN Resources Portal, and search for boxes: LXPLUS and Linux, AFS Workspaces, EOS/CERNBox.
2. Subscribe to LXPLUS and Linux.
3. Subscribe and setup your AFS Workspaces: you can have up to 10GB in /afs/cern.ch/user/<initial>/<username> and up to 100GB in /afs/cern.ch/work/<initial>/<username>. You can set these limits from the Settings in the "AFS Workspace".
4. Subscribe to EOS/CERNBox and login to cernbox: https://cernbox.cern.ch/. This will allow you access to /eos/user/<initial>/<username> with up to 1TB of space.

Users are recommended to setup code in their AFS Workspace areas and use their EOS/CERNBox for long term data storage. A simple script is provided to setup the relevant software dependencies in the LXPLUS environment.

source lxplus_setup.sh

Setting up on local machine with Docker

An el9 Docker container which mimics the lxplus environment is available from DockerHub.

A repository containing a script to easily run the container and mount cvmfs is available from github.com/benw22022/el9-cvmfs-docker

To get started do:

git clone https://github.com/benw22022/el9-cvmfs-docker.git
cd el9-cvmfs-docker/
./run_container /path/to/FPFSim

This will automatically pull and start the container and copy the .bashrc file which mounts cvmfs when the container starts.

As mentioned, this software relies upon the HEP_HPC library. A precompiled version of this code is provided in the repository. To set this up run

# You only need to do this once
cd FPFSim
tar -xvf HEP_HPC-el9.tar

Then to set up the environment do

source FPFSim/local_setup.sh

To compile the code

• Create a new directory to contain the executables (assume the path is /path/to/build).
• Assume the path to the source code is /path/to/source.
• To compile, you need to go to the build directory cd /path/to/build.
• And then cmake -S /path/to/source -B /path/to/build.
• Finally, make or make install.

The minimal software requirements are:

• Geant4 v4_10_6_p01c
• ROOT v6_22_06a
• HEP_HPC v0_14_01
• HDF5 v1_10_0+

These are automatically satisfied once the lxplus_setup.sh script is sourced. There is no longer an explicit GENIE dependency. However, the input GENIE ghep files need to be converted in the gst format (plain ROOT tree). The conversion can be perfomed with the native GENIE utility gntpc.

Run the simulation

Once the code has been compiled, the simulation can be run by passing a macro file to the FPFSim executable:

./FPFSim /path/to/macro.mac

Several examples of macros are available in the macros directory. The detector geometries can be easily imported by including one of the macros in macros\geometry_options. If no macro is passed as argument, the default is macros\vis.mac which simply displays the current geometry.

Single particles

There are several .mac macros in macros\single_particle directory: LAr_e-_mono.mac, LAr_mu-_mono.mac, etc. As denoted by the name, they're used to simulate single e-/mu-/... particles inside the FLArE volume. To run a simulation, just do ./FPFSim macros/single_particle/LAr_e-_mono.mac. If you want to modify the energy you intend to simulate, modify the parameters inside the mac scripts.

Neutrino events

Neutrino events are generated by reading nu-Ar interaction vertexes from GENIE output files and transposing the final states particles in Geant4. These GENIE gst files are available for all users in \eos\user\m\mvicenzi\genie. Example macros can be found in macros: numu_genie.mac, nue_genie.mac, nutau_genie.mac.

Background events

Background particles entering the FPF (muons, neutrons) are generated using the fluxes produced by the CERN-FLUKA team simulations. Events are sampled via summary histograms available in backgrounds\background_input.root. An example macro can be found in macros: backgrounds.mac.

Long-lived particle events

BSM long-lived particle (LLP) events made by event generators like FORESEE output files in the HepMC3 format. An example dark photon HepMC3 file can be found here:

/afs/cern.ch/user/b/bewilson/work/public/hepmc/events_14TeV_m0.3548GeV_c1e-06_to_mu_mu_s1.hepmc3

An example macro for running over this file can be found in macros/dark_photon_hepmc.mac.

Older versions of FORESEE output events in the HepMC2 format. To run over HepMC2 files set the option /gen/hepmc/useHepMC2 true in your macro. An example macro can be found in macros/dark_photon_hepmc2.mac.

Macro commands

Geometry

Command	Description	Default
/det/saveGdml	option for saving detector geometry in a GDML file, run before /run/initialize	false
/det/fileGdml	option for specifying the GDML file name, run before /run/initialize	FPF_geo.gdml
/det/checkOverlap	check overlap of volumes during detector construction, run before /run/initialize	false
/det/addFLArE	option for adding the FLArE detector, run before /run/initialize	true
/det/addFORMOSA	option for adding the FORMOSA detector, run before /run/initialize	true
/det/addFASERnu2	option for adding the FASERnu2 detector, run before /run/initialize	true
/det/faser/addFASER2	option for adding the FASER2 detector, run before /run/initialize	true
/det/flare/addFLArEPos	position of the FLArE detector, run before /run/initialize	0 0 4300 mm
/det/flare/material	option for detector material, choose LAr or LKr, run before /run/initialize	LAr
/det/flare/module	option for tpc module option, choose single or 3x7, run before /run/initialize	single
/det/flare/field	option for setting the magnetic field value in FLArE HadCather and Muon Finder	1 T
/det/flare/useBabyMIND	option for using BabyMIND instead of the legacy FLArE HadCather and Muon Finder	false
/det/babymind/blockSequence	option for BabyMIND module sequence	|MMMMD||DMMMD||DMMMMD||MMDMMD||MMDMMD||MDMDMD||DMMMD|
/det/babymind/magnetPlateThickness	option for BabyMIND magnet plate thickness	30 mm
/det/babymind/magnetPlateSizeX	option for BabyMIND magnet plate size x	3 m
/det/babymind/magnetPlateSizeY	option for BabyMIND magnet plate size y	2 m
/det/babymind/magnetCentralPlateY	option for BabyMIND central magnet plate height (y)	1 m
/det/babymind/slitSizeX	option for BabyMIND magnet plate slit size x	2.8 m
/det/babymind/slitSizeY	option for BabyMIND magnet plate slit size y	10 mm
/det/babymind/fieldStrength	option for BabyMIND magnetic field strength	1.5 T
/det/babymind/verticalNbars	option for number of vertical bars in BabyMIND modules	16
/det/babymind/horizontalNbars	option for number of horizontal bars in babyMIND modules	96
/det/babymind/barThickness	option for BabyMIND scintillator bar thickness	7.5 mm
/det/babymind/verticalBarSizeX	option for BabyMIND vertical scintillator bar size x	21 cm
/det/babymind/verticalBarSizeY	option for BabyMIND vertical scintillator bar size y	2 m
/det/babymind/horizontalBarSizeX	option for BabyMIND horizontal scintillator bar size x	3 m
/det/babymind/horizontalBarSizeY	option for BabyMIND horizontal scintillator bar size y	3 cm
/det/babymind/magnetToScinSpacing	option for BabyMIND magnet plate to scintillator module spacing	15 mm
/det/babymind/magnetToMagnetSpacing	option for BabyMIND magnet plate to magnet plate spacing	20 mm
/det/babymind/blockToBlockSpacing	option for BabyMIND block to block spacing	30 mm
/det/babymind/blockPadding	option for BabyMIND block padding size	100 mm
/det/formosa/addFORMOSAPos	position of the FORMOSA detector, run before /run/initialize	0 0 13870 mm
/det/fasernu/addFASERnu2Pos	position of the FASERnu2 detector, run before /run/initialize	0 0 22023 mm
/det/faser/addFASER2Pos	position of the FASER2 detector, run before /run/initialize	0 0 42636 mm
/det/faser/magnetGeom	option for FASER2 magnet geometry, choose SAMURAI or CrystalPulling	SAMURAI
/det/faser/magnetField	option for setting the FASER2 magnetic field value	1 T
/det/faser/magnetWinX	option for SAMURAI magnet window size along X axis	3.0 m
/det/faser/magnetWinY	option for SAMURAI magnet window size along Y axis	1.0 m
/det/faser/magnetWinZ	option for SAMURAI magnet window size along Z size	4.0 m
/det/faser/yokeThickX	option for SAMURAI yoke thickness along X axis	1.5 m
/det/faser/yokeThickY	option for SAMURAI yoke thickness along Y axis	2.0 m
/det/faser/magnetNumber	option for number of CrystalPulling magnets	3
/det/faser/magnetInnerR	option for CrystalPulling magnet inner radius	0.8 m
/det/faser/magnetOuterR	option for CrystalPulling magnet outer radius	1.2 m
/det/faser/magnetLengthZ	option for CrystalPulling magnet size along Z axis	1.25 m
/det/faser/magnetGap	option for gap length (along Z) between CrystalPullin magnets	0.5 m
/det/faser/trackingNumber	option for number of FASER2 tracking stations in each assembly	6
/det/faser/trackingScinThick	option for scintillator bar thickness (along Z) in tracking layers	1.0 cm
/det/faser/trackingGap	option for gap length (along Z) between tracking stations, and gap to magnet	0.5 m
/det/faser/fillCaloAndWall	option to fill FASER2 iron wall and calorimeter placeholder volumes with metal if true. Otherwise, fill with air to save having to compute the additional material interactions.	true

Event generators

Command	Description
/gen/select	option to select the generator, choices are gun,genie,hepmc,background
/gen/genie/genieInput	if genie is selected, give which .gst.root file to read GENIE events
/gen/genie/genieIStart	if genie is selected, give the start position of the file to read GENIE events
/gen/genie/randomVtx	if genie is selected, randomize vertex position in the fiducial volume
/gen/bkg/backgroundInput	if background is selected, give which file to sample background events
/gen/bkg/backgroundWindow	iif background is selected, set time window for background extraction
/gen/hepmc/useHepMC2	if hepmc is selected, set true to expect HepMC2 file format (instead of HepMC3)
/gen/hepmc/hepmcInput	if hepmc is selected, give which .hepmc file to read events from
/gen/hepmc/vtxOffset	if hepmc is selected, give an x, y, z offset to each vertex. Useful if you need to align events from another generator (i.e. FORESEE) with this G4 simulation.
/gen/hepmc/placeInDecayVolume	if hepmc is selected, will automatically translate vertex into the FASER2 decay volume. Assumes that the vertices start from (0,0,0). If this is not the case then /gen/hepmc/vtxOffset must also be set.

Analysis

Command	Description
/histo/fileName	option for AnalysisManagerMessenger, set name of the file saving all analysis variables
/histo/saveHit	if true save info for all hits, false in default to save space
/histo/saveTrack	if true save info for all tracks, false in default, requires \tracking\storeTrajectory 1
/histo/save3DEvd	if true save 3D spatial distribution of energy deposition, false in default
/histo/save2DEvd	if true save 2D spatial distribution of energy deposition, false in default
/histo/circleFit	if true run circle fitting and save information in output, false in default to save space
/histo/addDiffusion	if toy diffuse energy, if single diffuse single electron, false in default without diffusion

How to save an event display with high resolution using the DAWN Event Display

There is this tutorial for use at the October 2003 Fermilab Geant4 Tutorial.

• Add /vis/open DAWNFILE to the mac file, after running a pass of simulation you'll find a ".prim" files suitable for viewing in DAWN.
• Run ~/dune_data/app/dawn_3_91a/dawn -d filename.prim, and it will generate a high resolution picture with the format of EPS.