================================================
||    T R G E M 4     R E A D M E  v. 0.1.0   ||
||          - - - - - - - - - - - - -         ||
||               Florian ZENONI               ||
================================================

This program is a rather simple Geant4 application that evaluates the sensitivity of a gas detector (Triple GEM or RPC) to an incident beam of photons or neutrons.

 1- GEOMETRY DEFINITION

  The Geometry is constructed in the TrGEMDetectorConstructiobn class.
  The setup consists of a sequence of parallelepipeds with a trapezoidal base, oriented along the beam axis.
  The set of materials was chosen to reproduce as much as possible geometry of Triple GEMs that will be installed in the GE1/1 stations of CMS detector. Another currently available choice for the geometry includes RPC setup, in order to reproduce literature results.

 2- PHYSICS LIST

  Physics list (PL) must be chosen accordingly to the particle that is chosen for the simulation. It is necessary to include the PL in the TrGEMG4.cc file.

  QGSP_FTFP_BERT is available for photons: it takes care of the electromagnetic physics. 

 3- PRIMARY GENERATOR

  The primary generator is defined in the TrGEMPrimaryGeneratorAction class. The default kinematics is a 2 GeV photon having its source at z = -5 cm from the center of the World volume, heading perpendicularly to the detector's surface.
  This default setting can be changed via the Geant4 built-in commands of the G4GeneralParticleSource class.

 4- DETECTOR RESPONSE

  This program demonstrates the scoring of a simple variable directly in the sensitive detector class. No actual usage of the G4Hit class is implemented.

  It is in the GasGapSensitiveDetector that the sensitivity information is collected. This same information is then saved and stored in a ROOT file thanks to the Analysis function.

  Actually two different definitions of sensitivity are offered:
    a- If the energy released in the GasGap n.1 is greater than 5 times the effective energy to generate a pair electron-ion in Ar:CO2:CF4 (45:15:40) than driftDep is set to True. If this condition is not met, the same algorithm is applied for GasGap n.2: if the energy is high enough, then transferDep is set as True.
    b- An event is defined as sensitive if a charged particle appears in GasGap n.1 or n.2. The boolean associated to this definition is called neutSensitive.

  Definition b has proven to be more faithful to experimental cross-sections in the photon case. No such results have been produced so far for the neutrons.