hadronic/Hadr10/README.md

0001 \page ExampleHadr10 Example Hadr10
0002
0003 This is an example that aims to test the treatment of decays in Geant4.
0004 In particular, we want to test the decays of the tau lepton, charmed and
0005 bottom hadrons, and the use of pre-assigned decays.
0006
0007 Note that pre-assigned decays are decays that are usually specified by
0008 Monte Carlo event generators. For simplicity, and to avoid dependencies
0009 on external code, in this test we don't use any MC generator, and we
0010 pre-assign decays by hand (using the Geant4 decay table: this is done
0011 in the method SteppingAction::UserSteppingAction). But this does not
0012 change anything regarding the testing of the pre-assignment mechanism
0013 of Geant4.
0014
0015 The set-up is very simple: a cylindrical layer, 2 meter long, whose radii
0016 (inner and outer) and material can be specified via UI commands. By default,
0017 the material is Beryllium, with inner radius of 9 mm and outer radius of
0018 11 mm (i.e. the default thickness is 2 mm). In the rest of the world volume,
0019 is filled with G4_Galactic material (i.e. very low density gas).
0020 There is an uniform and constant magnetic field along the z-axis, whose
0021 value is set via UI command.
0022
0023 The primary particle, tau- by default, is shot along the x-axis, starting
0024 from the center (0, 0, 0).
0025 Its kinetic energy, by default 500 GeV, can be set via UI command.
0026
0027 All secondaries are killed immediately, so only the primary particle
0028 is studied.
0029
0030 The only interesting part of this example is the SteppingAction.
0031 The decay of the primary particle is pre-assigned there.
0032 When the primary particle decays, the properties of the decay -
0033 position, momentum, energy, etc. of the particle at the moment
0034 of the decay - are collected and then used to:
0035 -  compute the difference between the "MC-truth" decay radius
0036    (defined as the radius at which the primary would have decayed
0037     if there were no magnetic field and interactions with matter,
0038     i.e. no energy loss and no multiple scattering) and the real
0039    decay radius
0040 -  compute the angular deflection (in degrees) between the initial
0041    direction of the primary and its final direction at the moment
0042    it decays
0043 -  the energy loss (i.e. the difference between the initial kinetic energy
0044    of the primary and the its kinetic energy at the moment of the decay)
0045 -  the energy-momentum violation of the decay (i.e. the difference between
0046    the sum of the 4-momenta of the decay products and the 4-momentum of
0047    primary particle at the moment of its decay).
0048 Some of these information are printed out for each decay, and a summary
0049 statistics is printed out at the end of the application.
0050
0051 Look for the string "***LOOKHERE***" for those parameters/options that
0052 are hardwired in the code (i.e. not available via UI command).
0053
0054 This example uses the physics list factory, therefore you can specify
0055 the reference physics list you want to use via the PHYSLIST
0056 environmental variable (by default, if you don't set it, the FTFP_BERT
0057 physics list is used).
0058
0059 To build this example:
0060
0061     mkdir Build; cd Build
0062     cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo \
0063           -DGeant4_DIR=/path-to-geant4-libraries ../.
0064     make
0065
0066 To run it:
0067
0068     ./Hadr10 hadr10.in
0069
0070 which shoots 500 GeV TeV particles - one run of 10'000 events for each
0071 type of particle - along the x-axis, and print out some information
0072 regarding their decays, as well as some summary information at the end
0073 of each run.