$Id: README,v 1.10 2009/11/21 00:22:55 perl Exp $

    =========================================================
    Geant4 - an Object-Oriented Toolkit for Simulation in HEP
    =========================================================

                       Extended Example A01
                       -------------------- 

  Example A01 implements a double-arm spectrometer with wire chambers, 
  hodoscopes and calorimeters.  Event simulation and collection are 
  enabled, as well as event display and analysis.


  1. GEOMETRY

     The spectrometer consists of two detector arms.  One arm provides 
     position and timing information of the incident particle while the 
     other collects position, timing and energy information of the particle
     after it has been deflected by a magnetic field centered at the 
     spectrometer pivot point.
 
       - First arm:  box filled with air, also containing:

           1 hodoscope (15 vertical strips of plastic scintillator)
           1 drift chamber (5 horizontal argon gas layers with a 
                            "virtual wire" at the center of each layer)

       - Magnetic field region: air-filled cylinder which contains
                                the field

       - Second arm:  box filled with air, also containing:

           1 hodoscope (25 vertical strips of plastic scintillator)
           1 drift chamber (5 horizontal argon gas layers with a 
                            "virtual wire" at the center of each layer)
           1 electromagnetic calorimeter: 
                 a box sub-divided along x,y and z
                 axes into cells of CsI 
           1 hadronic calorimeter: 
                 a box sub-divided along x,y, and z axes
                 into cells of lead, with a layer of 
                 plastic scintillator placed at the center 
                 of each cell


  2. PHYSICS

     This example uses the following physics processes:

       - electromagnetic:
           photo-electric effect
           Compton scattering
           pair production
           bremsstrahlung
           ionization
           multiple scattering
           annihilation

       - decay

       - transportation in a field

     and defines the following particles:
        geantino, charged geantino, gamma, all leptons, 
        pions, charged kaons

     Note that even though hadrons are defined, no hadronic processes 
     are invoked in this example.


  3. EVENT:

     An event consists of the generation of a single particle which is 
     transported through the first spectrometer arm.  Here, a scintillator 
     hodoscope records the reference time of the particle before it passes
     through a drift chamber where the particle position is measured. 
     Momentum analysis is performed as the particle passes through a magnetic
     field at the spectrometer pivot and then into the second spectrometer 
     arm.  In the second arm, the particle passes through another hodoscope
     and drift chamber before interacting in the electromagnetic calorimeter.
     Here it is likely that particles will induce electromagnetic showers.  
     The shower energy is recorded in a three-dimensional array of CsI 
     crystals.  Secondary particles from the shower, as well as primary 
     particles which do not interact in the CsI crystals, pass into the 
     hadronic calorimeter.  Here, the remaining energy is collected in a 
     three-dimensional array of scintillator-lead sandwiches.

     Several aspects of the event may be changed interactively by the user:

       - initial particle type
       - initial momentum and angle
       - momentum and angle spreads
       - type of initial particle may be randomized
       - strength of magnetic field
       - angle of the second spectrometer arm


  4. DETECTOR RESPONSE:

     All the information required to simulate and analyze an event is 
     recorded in HITS.  This information is recorded in the following 
     sensitive detectors:

       - hodoscope: 
           particle time
           particle position
           strip ID

       - drift chamber: 
           particle time
           particle position
           layer ID
 
       - electromagnetic calorimeter: 
           particle position 
           energy deposited in cell
           cell ID
  
       - hadronic calorimeter:   
           particle position 
           energy deposited in cell
           cell ID


  5. VISUALIZATION:
  
     Simulated events can be displayed on top of a representation of the spectrometer.

     vis.mac outputs HepRep version 1 files suitable for viewing in HepRApp or WIRED4.
     Change the /vis/open line from HepRepFile to DAWNFILE to instead
     make .prim files suitable for viewing in DAWN.

     heprep2-000-gz.mac outputs a series of gzipped HepRep version 2 files
     each containing a single event, suitable for viewing in HepRApp or WIRED4

     heprep2zip.mac outputs a single zip file that unzips to a series of
     HepRep version 2 files, each each containing a single event (unzip
     the single file by hand, then view the resulting individial HepRep files).

     heprep2-000-zip.mac outputs a series of zipped HepRep version 2 files
     each containing a single event (not yet viewable unless you
     explicitly unzip them before viewing).

     heprep2.mac outputs a HepRep version 2 file with multiple events
     appended to a single file in an experimental manner

     heprep2gz.mac outputs a HepRep version 2 file with multiple events
     appended to a single file in an experimental manner

     Any of the heprep mac files above with the name bheprep (for instance
     bheprep2zip.mac) will write a Binary HepRep version 2 file, readable only
     by WIRED4 (not by HepRApp).


  6. ANALYSIS:

     This example implements an AIDA-compliant analysis system which
     creates histograms, ntuples and plotters.  If you have built Geant4 with
     the option to use anlaysis (answering yes to the appropriate question in
     ./Configure -build), then at the completion of a simulation run,
     a file A01.aida is produced which contains these data structures.
     This file can be used as an input to the Java Analysis Studio (JAS) which allows
     the histograms and ntuples to examined, manipulated, saved and printed.
     For further details, see README.JAIDA.