Documentation of g4sbs

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Documentation page for g4sbs

This page is maintained by the UConn group (Andrew Puckett) and as of July 22, 2015 is based on the "uconn_dev" branch of g4sbs on github.

Getting the code and building the program

Prerequisites

  • Working ROOT installation. g4sbs is not yet compatible with root version 6!
  • Working GEANT4 installation. For the uconn_dev branch, g4sbs is only compatible with GEANT4 version 10.0 and later.
  • cmake (also required in any case to build GEANT4).

Note on GEANT4 build options:

  • GEANT4_INSTALL_DATA=ON is needed
  • On Mac OS X, I have built GEANT4 against Qt version 5.3.2. Newer versions of Qt seem to cause GEANT4 Qt-based visualization to crash.

Downloading the repository

The code is hosted on a github repository owned by JLab. To clone via ssh (preferred method on JLab batch farm), do:

git clone git@github.com:JeffersonLab/g4sbs.git

For this method to work, the ssh public key on the machine where you want to get the code must be added to your github account (see Guide to generating ssh keys and adding to your github.com account.)

Cloning the repository defaults to the "master" branch. This page documents the "uconn_dev" branch, which will soon be merged into the master branch. To change to the "uconn_dev" branch, do:

git checkout uconn_dev

Building the program

Create a "build" directory that is parallel to the "g4sbs" source directory (this is not strictly required, but the build directory must be separate from the "g4sbs" directory. The following instructions assume that "build" is parallel to "g4sbs":

mkdir build
cd build
cmake ../g4sbs
make

If successful, the g4sbs executable and several other files and folders will be created in the "build" directory.

How to run the program

g4sbs works in two different modes, batch mode or interactive mode. In interactive mode, visualization of the geometry and events is possible. To run in interactive mode, do

./g4sbs

This will launch an interactive g4sbs session which, depending on your GEANT4 build, might be a csh terminal, a Qt GUI, or something in between. The Qt GUI in particular has a complete help menu:

G4sbs QtGUI.png


To run g4sbs in batch mode, do one of the following:

./g4sbs file.mac OR
./g4sbs preinit.mac postinit.mac,

where each ".mac" file is a text file containing valid GEANT4 and/or g4sbs commands, used to configure the simulation. If g4sbs is invoked with one command-line argument as in the first example, it will execute all the commands in "file.mac" after G4RunManager::Initialize(). If g4sbs is invoked with two command line arguments as in the second example, it will execute the commands in "preinit.mac" before G4RunManager::Initialize() and the commands in "postinit.mac" after G4RunManager::Initialize(). As detailed below, this feature was added to make it possible for the user to disable optical photon production via the Cherenkov and Scintillation processes without re-compiling the code, and a long-standing GEANT4 bug prevents disabling of the scintillation process via the standard /process/inactivate command.

g4sbs commands

This section documents all g4sbs commands.

  • /g4sbs/run nevent: runs the simulation with nevent events. Note that this command forces building or rebuilding of the geometry, in contrast to /run/beamOn, which does not re-initialize the G4 kernel. Presently, g4sbs will crash if the /g4sbs/run command is invoked more than once in a g4sbs session (bug is under investigation), meaning that configuration changes require separate simulation jobs.
  • /g4sbs/gemconfig: expects one integer argument, defines BigBite GEM layout, possible values are 1 (default), 2, 3
  • /g4sbs/CDetconfig: defines configuration of the coordinate detector. This command is obsolete and currently has no effect
  • /g4sbs/ECALmap: Accepts one string argument which is the name of a text file listing active ECAL cells (rows, columns). File is assumed to be located in the database/ subdirectory. This command is obsolete and currently has no effect
  • /g4sbs/filename: Define output ROOT file name.
  • /g4sbs/sigmafile: File containing GEM coordinate resolutions by chamber ID number. This command is obsolete and currently has no effect
  • /g4sbs/target: Choose target type. Possible values currently include:
    • LH2: liquid hydrogen target with scattering chamber and vacuum snout. Density fixed at 0.071 g/cm<math>^3</math>
    • LD2: liquid deuterium target with scattering chamber and vacuum snout. Density fixed at 0.1624 g/cm<math>^3</math>
    • H2: Hydrogen gas target, fixed pressure of 10.5 atm at 300 K
    • 3He: Helium-3 gas target, fixed pressure of 10.77 atm at 300 K.
    • neutron: Free neutron target, fixed pressure of 10.5 atm at 300 K.
    • Note: All gas targets are currently enclosed in a GE180 glass cell with endcap thickness of 0.126 mm and wall thickness of 1.61 mm
  • /g4sbs/kine: Choose kinematics for event generator. In all cases, unless otherwise noted, interaction vertex is generated flat assuming a square raster centered at (x,y)=(0,0) with user-defined raster size in x and y, and z along the target length. Currently available kinematics types are:
    • elastic: elastic electron-nucleon scattering. Electron polar and azimuthal angles are generated flat in <math>\cos \theta</math> and <math>\phi</math> within user-defined limits, everything else calculated from energy-momentum conservation. Cross section according to Kelly fit for GEp, GMp, GMn and Hall A GEn collaboration fit of GEn data. Behavior depends on target type:
      • For H2 or LH2 or neutron targets: elastic electron scattering from free proton (or neutron) at rest
      • For LD2 or <math>^3</math>He targets: Quasi-elastic electron-nucleon scattering with Fermi motion simulated by sampling the initial nucleon momentum from the momentum distribution in deuterium or <math>^3</math>He.
    • flat: Generate electron angles flat in <math>\cos \theta</math>, <math>\phi</math>, and <math>E'</math>. Generate final nucleon assuming that the outgoing nucleon absorbs all of the three-momentum transfer from the electron. Not clear how much sense this makes physically.
    • dis: Deep inelastic scattering. Generate scattered electron angles flat within user-defined limits, generate <math>E'</math> flat in <math>0 \le E' \le E</math>. Reject event if not kinematically allowed. Don't generate any final hadrons. Cross section based on CTEQ6 PDFs and neglect of longitudinal structure function <math>F_L = 0</math>
    • beam: Beam kinematics. Generate beam electrons 5 meters upstream of the target with (x,y) according to normal raster size definitions.
    • sidis: Single-hadron semi-Inclusive deep inelastic electron-nucleon scattering (SIDIS) <math>N(e,e'h)X</math>. Generate outgoing electron and hadron angles flat in <math>\cos \theta</math> and <math>\phi</math> within user-defined limits. Generate outgoing electron and hadron energies flat within user-defined limits. Check four-momentum conservation and reject event/try again until a kinematically allowed event is returned. Compute cross section according to CTEQ6 PDFs and DSS2007 fragmentation functions. Assume flavor-independent Gaussian transverse momentum widths for PDF and fragmentation function. Neglect the longitudinal cross section for SIDIS. On output, normalize phase-space volume for event generation according to the efficiency for generating kinematically allowed events. Hadron <math>h = \pi^+</math>, by default. See /g4sbs/hadron for available hadrons in the event generator.
    • wiser: Single inclusive hadron production. Generate outgoing hadron angles and energy flat within user-defined limits, compute "Wiser" cross section. See /g4sbs/hadron for available hadrons for this generator. Cross section calculation only defined for <math>\pi^\pm, \pi^0</math>.
    • gun: Generic particle gun. Generate outgoing particle angles and energy according to user-defined limits. Vertex is generated according to usual prescription. Any valid GEANT4 particle type can be selected.
  • /g4sbs/hadron: Choose hadron type for SIDIS and/or Wiser generators. Valid choices are:
    • pi+: positive pion, valid for sidis, wiser
    • pi-: negative pion, valid for sidis, wiser
    • pi0: neutral pion, valid for sidis, wiser
    • K+: positive kaon, valid for sidis (Wiser will generate but not calculate cross section)
    • K-: negative kaon, valid for sidis (Wiser will generate but not calculate cross section)
    • p: proton, valid for sidis (Wiser will generate but not calculate cross section)
    • pbar: antiproton, valid for sidis (Wiser will generate but not calculate cross section)
  • /g4sbs/48d48field: Expects integer argument. Turn on (1) or off (0) SBS uniform magnetic field.
    • Turning ON (1) adds a uniform magnetic field located in the gap of the SBS magnet, and adds it to the "global field" object in G4SBSDetectorConstruction. If the "fUseGlobalField" flag of "G4SBSDetectorConstruction" is false, which is the case by default, the "fUseLocalField" flag is set for the "G4SBSHArmBuilder" class which defines the SBS geometry, which causes a local magnetic field to be associated with the air gap inside the SBS dipole magnet. Note: This command should never be used in combination with /g4sbs/tosfield below, as it will cause the uniform magnetic field to be added in superposition with the TOSCA field, approximately doubling or canceling the magnetic field in the gap, depending on the overall scale factors applied.. See "Setting up the magnetic field" below for a more detailed discussion of the way magnetic fields are handled.
    • Turning OFF (0) deletes the uniform magnetic field from the global field if it exists, and sets the "local field" flag for "HArmBuilder" to false if and only if the "fUseGlobalField" flag of G4SBSDetectorConstruction is true, which prevents the uniform field from being created in "HArmBuilder"
  • /g4sbs/bbfield: Expects integer argument. Turn on (1) or off (0) BigBite magnetic field. Requires BigBite field map file (see "setting up the magnetic field" below).
    • Turning ON (1) creates a new "G4SBSBigBiteField" object and adds it to the global field. If the "fUseGlobalField" flag of "G4SBSDetectorConstruction" is false, which is the case by default, the "fUseLocalField" flag is set for the "G4SBSEArmBuilder" class which defines the BigBite geometry. The bigbite magnetic field map is then assigned to the mother logical volume containing the BigBite magnet and detectors.
    • Turning OFF (0) deletes the bigbite field from the global field object, and sets the "local field" flag for "EArmBuilder" to false iff the "global field" flag is set.
  • /g4sbs/tosfield: Use global field from TOSCA field map file. Expects string argument equal to file name of map file. Requires SBS TOSCA field map file. See "setting up the magnetic field" below for more details. Note: invoking /g4sbs/tosfield is currently the only mechanism to set the "global field" flag to true. Invoking this command sets the "local field" flags for "EArmBuilder" and "HArmBuilder" to false.
  • /g4sbs/shootgeantino: Expects a boolean argument. If true, shoot a geantino instead of an electron.
  • /g4sbs/invertfield: Expects a boolean argument. If true, changes the sign of all global magnetic fields (also changes the sign of local magnetic fields).
  • /g4sbs/totalabs: boolean argument. If true, causes BigBite and SBS magnet materials to be total absorbers using G4UserLimits. Useful to speed up the simulation in applications such as acceptance and rate calculations.
  • /g4sbs/targlen: Sets target length along beam direction. Requires a value and a unit.
  • /g4sbs/targden: Sets target density. Requires a value and a unit. Note: the current behavior of the code is that this command has no effect, because the densities of target materials are hard-coded in G4SBSDetectorConstruction::ConstructMaterials()
  • /g4sbs/targpres: Sets target pressure. Applies to gas targets. Requires a value and a unit. Note: the current behavior of the code is that this command has no effect, because the densities of target materials are hard-coded in G4SBSDetectorConstruction::ConstructMaterials().
  • /g4sbs/beamcur: Beam current. Requires a value and a unit. Currently used in the normalization of events from a cross-section to an event rate.
  • /g4sbs/runtime: Run duration Requires a value and a unit. Used to normalize events from cross section --> rate --> number of counts. Unit must be a valid time unit defined in G4SystemOfUnits.hh ("hour" "day" "year" do NOT work).
  • /g4sbs/rasterx: Define horizontal raster size. Requires a value and a unit.
  • /g4sbs/rastery: Define vertical raster size. Requires a value and a unit.
  • /g4sbs/beamE: Define beam energy. Requires a value and a unit.
  • /g4sbs/bbang: Define BigBite/electron arm angle (also applies to ECAL in the GEP configuration). Requires a value and a unit.
  • /g4sbs/bbdist: Define BigBite/electron arm distance from target. Requires a value and a unit.
    • In experiments using BigBite, this defines the distance from the target center (origin of global coordinates) to the front face of the magnet yoke.
    • In the GEP experiment using ECAL, this defines the distance from the target center to the back of the lead-glass blocks of ECAL (currently all assumed to be 40 cm thick). The front of the lead-glass is therefore 40 cm closer to the target than the value defined using this command.
  • /g4sbs/sbsang: Define SBS angle. Requires a value and a unit.
  • /g4sbs/hcaldist: Distance from the target center to the front surface of HCAL. Requires value and unit.
  • /g4sbs/48D48dist: Distance from target center to front face of SBS magnet yoke. Requires value and unit.
  • /g4sbs/gemres: Set GEM coordinate resolution <math>1\sigma</math>. Local x and y coordinates of hits in GEM detectors are subject to Gaussian smearing with this <math>\sigma</math>. Requires value and unit.

"Pre-init" vs "Post-init" commands

Setting up the magnetic field

Output ROOT tree structure

Useful links

Git Documentation Github.com homepage for g4sbs