SWGuideFastSimSimHitsAndTracks < CMSPublic

CMSPublic Web>SWGuide>SWGuideFastSimulation>SWGuideFastSimSimHitsAndTracks (2015-04-27, LukasVanelderen) (raw view)
---+!! !SimHits, !SimTracks, and !SimVertices in !FastSim

%TOC%

---+ !SimTrack and !SimVertex collections

The !SimTrack and !SimVertex collections summarise the trajectories of particles through the detector.

One part of the !SimTrack and !SimVertex collection comes from the particles provided by the generator.
For each generator particle, the origin vertex is stored as a !SimVertex,
and the properties of the particle at the origin vertex are stored as !SimTrack.
   * These !SimVertices and !SimTracks are produced in the function
   =FBaseSimEvent::fill(const std::vector<SimTrack>& simTracks,const std::vector<SimVertex>& simVertices)=
   ([[https://github.com/cms-sw/cmssw/blob/CMSSW_7_4_0/FastSimulation/Event/src/FBaseSimEvent.cc#L121][link to code]])
   * which is caled inside
   =FamosManager::reconstruct=
   ([[https://github.com/cms-sw/cmssw/blob/CMSSW_7_4_0/FastSimulation/EventProducer/src/FamosManager.cc#L170][link to code]])

The remaining part of the !SimTrack and !SimVertex collections
represent decays of particles and interactions between particles and detector material.
The following interactions lead to creation of !SimVertices and !SimTracks:

   * *bremsstrahlung:* the interaction vertex is stored as !SimVertex, the photons are stored as !SimTracks, the new state of the electron is *not* stored as !SimTrack
   see
   [[https://github.com/cms-sw/cmssw/blob/CMSSW_7_4_0/FastSimulation/MaterialEffects/src/MaterialEffects.cc#L342][MaterialEffects::interact]]
   and
   [[https://github.com/cms-sw/cmssw/blob/CMSSW_7_4_0/FastSimulation/MaterialEffects/src/BremsstrahlungSimulator.cc#L16][BremsstrahlungSimulator::compute]]

   * *photon conversion:* (pair production): the interaction vertex is stored as !SimVertex, the electron positron pair is stored as two Simtracks</br>
   see
   [[https://github.com/cms-sw/cmssw/blob/CMSSW_7_4_0/FastSimulation/MaterialEffects/src/MaterialEffects.cc#L244][MaterialEffects::interact]]
   and
   [[https://github.com/cms-sw/cmssw/blob/CMSSW_7_4_0/FastSimulation/MaterialEffects/src/PairProductionSimulator.cc#L13][PairProductionSimulator::compute]]

   * *nuclear interactions:* two kinds of nuclear interactions are stored, elastic and inelastic ones
      * see
      [[https://github.com/cms-sw/cmssw/blob/CMSSW_7_4_0/FastSimulation/MaterialEffects/src/MaterialEffects.cc#L281][MaterialEffects::interact]]
      and
      [[https://github.com/cms-sw/cmssw/blob/CMSSW_7_4_0/FastSimulation/MaterialEffects/src/MaterialEffects.cc#L281][NuclearInteractionSimulator::compute]]
      * elastic nuclear interactions: only if the angle between the intial and the final state particle is large enough,
      the interaction vertex is stored as !SimVertex and the final state particle as !SimTrack ([[https://github.com/cms-sw/cmssw/blob/CMSSW_7_4_0/FastSimulation/MaterialEffects/src/NuclearInteractionSimulator.cc#L279][link to code]])
      * inelastic nuclear interactions: interaction vertex is stored as !SimVertex final state particles are stored as !SimTracks
      * if the particle is stopped, the end vertex is stored

   * *decays:* the decay vertex is stored as !SimVertex and the decay products as !SimTracks</br>
   see [[https://github.com/cms-sw/cmssw/blob/CMSSW_7_4_0/FastSimulation/TrajectoryManager/src/TrajectoryManager.cc#L460][PythiaDecays::particleDaughters]]

   *Filtering:* only those particles for which 
   [[https://github.com/cms-sw/cmssw/blob/CMSSW_7_4_0/FastSimulation/Event/src/KineParticleFilter.cc#L9][KineParticleFilter::isOKForMe]] 
   is true (tested at the origin vertex) are considered for simulation and may be stored as !SimTracks.

---+ !SimHits in tracker

* objects of class =PSimHit= ([[https://github.com/cms-sw/cmssw/blob/CMSSW_7_4_0/SimDataFormats/TrackingHit/interface/PSimHit.h][link to code]])

---++ Useful variables

* =int !PSimHit::trackId()= returns index of =SimTrack= in =SimTrackCollection= that produced the =SimHit=
* =int !PSimHit::particleType()= returns the Pdg id number of the =SimTrack= that produced the =SimHit=
* =float !PSimHit::energyLoss()= returns the energy lost by the =SimTrack= through ionisation in the silicon module at which the hit resides. This variable is used, during digitization, to determine the strength of the signal in the silicon sensors.

-- Main.LukasVanelderen - 2015-04-21
Topic revision: r4 - 2015-04-27 - LukasVanelderen
CMSPublic
Create a LeftBar
Public webs
- Cern Search
- TWiki Search
- Google Search
CMSPublic All webs