Gabriele Cosmo
255 lines
12 KiB
Plaintext
255 lines
12 KiB
Plaintext
-------------------------------------------------------------------
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=========================================================
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Geant4 - an Object-Oriented Toolkit for Simulation in HEP
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=========================================================
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Example Par02
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-------------
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This example is a simplified version of a Geant4-based fast simulation
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program written by Anna Zaborowska for Future Circular Collider (FCC)
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studies.
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This example shows how to do "track and energy smearing" in Geant4,
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in order to have a very fast simulation based on assumed detector
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resolutions.
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The geometry which is considered is a simplified collider detector set-up,
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inspired by ALEPH/ATLAS/CMS detectors. Although it is much simpler than
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a realistic detector, it is anyhow fairly complex and therefore build up
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from a GDML file, Par02FullDetector.gdml .
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In this example:
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- Particles with transverse momentum less than 1 MeV or pseudorapidity
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larger (in module) than 5.5 are neglected (i.e. the corresponding
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Geant4 track is killed as soon as it is created).
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- Any primary charged particle is smeared in the tracker as follows:
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its momentum is smeared according to a gaussian, with mean equal to 1.0
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and sigma taken from the momentum resolution of the CMS tracker
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(with ALEPH or ATLAS tracker as a possible alternative), and then placed
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at the end of the tracker, at the position that it would reach if
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normally transported (i.e. without smearing).
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- Any primary electron, or positron, or gamma is smeared in the
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electromagnetic calorimeter as follows: it is killed at the entrance
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of the electromagnetic calorimeter, with a deposited energy equal to
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the gaussian smearing (with mean equal to 1.0 and sigma taken from the
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energy resolution of the CMS electromagnetic calorimeter - with ALEPH or
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ATLAS electromagnetic calorimeter as a possible alternative) of its
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kinetic energy (at the entrance of the electromagnetic calorimeter).
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- Any primary hadron is smeared in the hadronic calorimeter as follows:
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it is killed at the entrance of the hadronic calorimeter, with a
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deposited energy equal to the gaussian smearing (with mean equal to 1.0
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and sigma taken from the energy resolution of the CMS hadronic
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calorimeter - with ALEPH or ATLAS hadronic calorimeter as a possible
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alternative) of its kinetic energy (at the entrance of the hadronic
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calorimeter).
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- The only competing physical processes with respect to the above physics
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parametrisations are the decays.
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Note: no electromagnetic processes;
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no momentum smearing in the tracker for secondary particles;
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secondary electrons, positrons, gammas in the electromagnetic
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calorimeter are killed (at the entrance) but without any
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energy deposition;
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secondary hadrons in the hadronic calorimeter are killed (at the
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entrance) but without any energy deposition.
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Below some details.
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1. Detector description
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-----------------------
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The geometry is read in from a GDML file, Par02FullDetector.gdml .
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The geometry is a simplified collider detector set-up used for the
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first FCC studies, inspired by ALEPH/ATLAS/CMS detectors.
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It is made of 4 main parts:
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- Tracker
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- Electromagnetic calorimeter
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- Hadronic calorimeter
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- Muon subdetector
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In this example, fast simulation parametrisation models exist for the
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first three subdetectors, but not for the Muon subdetector.
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The three parametrisation models:
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- Par02FastSimModelTracker : in the tracker
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- Par02FastSimModelEMCal : in the electromagnetic calorimeter
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- Par02FastSimModelHCal : in the hadronic calorimeter
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are build and bound to the respective subdetector (i.e. Geant4 regions)
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in the method: Par02DetectorConstruction::Construct() .
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Three configurations are possible for those parametrisation models:
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CMS-like, ALEPH-like, ATLAS-like.
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By default, the CMS configuration is used.
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2. Primary generation
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---------------------
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In this example we use a very simple primary generation action,
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Par02PrimaryGeneratorAction, that uses the G4ParticleGun.
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One single particle type, with a well defined energy, and in one fixed
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direction is used for each run: the corresponding values can be set via
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macro commands. See examplePar02.in as an example.
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For the FCC studies, Pythia8 events in HepMC format were used for the
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generation of the primary particles.
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3. Physics List
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---------------
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A special, ad-hoc physics list is used in this example, in order to have
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an ultra-fast parametrised simulation: for all particles, the only two
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physics processes that are assigned are the decay process and the fast
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simulation process.
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The following three fast simulation models are defined:
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- Par02FastSimModelTracker :
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- bound to the tracker
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(see the method Par02DetectorConstruction::Construct )
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- applicable to all charged particles
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(see the method Par02FastSimModelTracker::IsApplicable )
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- triggered in all cases (i.e. no kinematic constraints)
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(see the method Par02FastSimModelTracker::ModelTrigger )
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- does the following: place the particle at the tracking detector exit
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(at the place the particle would reach without smearing), and, only
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if the particle is a primary, it smears the momentum of the particle
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according to a gaussian, with mean equal to 1.0 and sigma taken from
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the momentum resolution of the CMS tracker (with ALEPH or ATLAS tracker
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as a possible alternative)
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(see the method Par02FastSimModelTracker::DoIt )
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- Par02FastSimModelEMCal :
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- bound to the electromagnetic calorimeter
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(see the method Par02DetectorConstruction::Construct )
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- applicable to electrons, positrons, gammas
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(see the method Par02FastSimModelEMCal::IsApplicable )
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- triggered in all cases (i.e. no kinematic constraints)
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(see the method Par02FastSimModelEMCal::ModelTrigger )
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- does the following: kill the particle at the entrance of the
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electromagnetic calorimeter, and, only if the particle is a primary,
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it deposits in the electromagnetic calorimeter an energy obtained
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by a gaussian smearing (with mean equal to 1.0 and sigma taken from the
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energy resolution of the CMS electromagnetic calorimeter - with ALEPH
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or ATLAS electromagnetic calorimeter as a possible alternative) of the
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particle kinetic energy (at the entrance of the electromagnetic
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calorimeter)
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(see the method Par02FastSimModelEMCal::DoIt )
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- Par02FastSimModelHCal :
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- bound to the hadronic calorimeter
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(see the method Par02DetectorConstruction::Construct )
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- applicable to all hadrons (i.e. particles made of quarks)
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(see the method Par02FastSimModelHCal::IsApplicable )
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- triggered in all cases (i.e. no kinematic constraints)
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(see the method Par02FastSimModelHCal::ModelTrigger )
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- does the following: kill the particle at the entrance of the
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hadronic calorimeter, and, only if the particle is a primary,
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it deposits in the hadronic calorimeter an energy obtained by a
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gaussian smearing (with mean equal to 1.0 and sigma taken from the
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energy resolution of the CMS hadronic calorimeter - with ALEPH
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or ATLAS hadronic calorimeter as a possible alternative) of the
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particle kinetic energy (at the entrance of the hadronic
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calorimeter)
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(see the method Par02FastSimModelHCal::DoIt )
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4. User actions, user information and user utility classes
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----------------------------------------------------------
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- Par02RunAction : run action used for initialization and termination
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of the run.
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- Par02EventAction : event action used for initialization and termination
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of the event.
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- Par02TrackingAction : tracking action used for killing particles with
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transverse momentum less than 1 MeV or
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pseudorapidity larger (in module) than 5.5
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(see method Par02TrackingAction::PreUserTrackingAction )
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and to store the information about the track at
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the end of the simulation of such a track
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(see method Par02TrackingAction::PostUserTrackingAction ).
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- Par02ActionInitialization : initialization of the primary generator class
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and all user-defined actions (i.e. the three
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classes above).
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- Par02PrimaryParticleInformation : utility class to store information
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associated with a primary particle.
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- Par02EventInformation : utility class to store information associated
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with a Geant4 event.
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- Par02DetectorParametrisation : a simple class used to provide the detector
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resolution and efficiency, according to the
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type of detector: tracker, electromagnetic
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calorimeter, hadronic calorimeter.
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There are 3 choices: CMS-like (default),
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ALEPH-like and ATLAS-like.
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The efficiency is currently set to 1.0 in
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all cases and not used.
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- Par02Smearer : a simple class that does the gaussian smearing, either
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of the momentum (in the tracker detector) or in energy
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(in the electromagnetic or hadronic calorimeter).
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5. Output
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---------
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The execution of the program (examplePar02) produces in output, at the end
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of a run, a Root file, by default named DefaultOutput.root, which contains
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3 histograms and one ntuple.
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The macro file examplePar02.in specifies one run made of 1000 events
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each consisting of one 50 GeV electron.
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By editing the file, one could select alternatively a run made of 1000
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events each consisting of one 100 GeV muon, or a run made of 1000 events
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each consisting of one 20 GeV pion- .
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See the class Par02Output for the definition of the 3 histograms and the
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ntuples. Here is a quick summary:
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- histogram of the ratio of the momentum smeared and the original momentum
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in the tracker (for primary charged particles);
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- histogram of the ratio of the smeared energy deposited and the original
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energy at the entrance in the electromagnetic calorimeter (for primary
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electrons, positrons and gammas);
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- histogram of the ratio of the smeared energy deposited and the original
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energy at the entrance in the hadronic calorimeter (for primary hadrons);
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- ntuple containing the "Monte-Carlo true" information regarding the
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primary, and the resolution, efficiency, smeared momentum (tracker),
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smeared energy (calorimeter) and impact position (calorimeter) of each
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subdetector (tracker, electromagnetic calorimeter, hadronic calorimeter)
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where the primary is parametrised (tracker and electromagnetic calorimeter
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in the case of primary electrons, positrons and gammas; tracker and
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hadronic calorimeter in the case of primary hadrons; tracker only for
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all other primary charged particles, e.g. muons).
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Note:
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- you do not need to have the Root package available to run this example,
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but you need it if you want to look at the histograms and the ntuple
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contained in the Root output file;
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- sensitive detectors and hits are not used in this example.
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6. How to build and run the example
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-----------------------------------
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- You need to have built the Geant4 persistency/gdml module by having set
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the -DGEANT4_USE_GDML=ON flag during the CMAKE configuration step,
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as well as the -DXERCESC_ROOT_DIR=<path_to_xercesc> flag pointing to
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the path where the XercesC XML parser package is installed in your system.
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- Compile and link to generate the executable (in your CMAKE build directory):
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% make
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- Execute the application:
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% examplePar02 examplePar02.in
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which produces one Root file: DefaultOutput.root .
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