$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.