Gabriele Cosmo
72 lines
3.2 KiB
Plaintext
72 lines
3.2 KiB
Plaintext
This is an example that aims to test the treatment of decays in Geant4.
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In particular, we want to test the decays of the tau lepton, charmed and
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bottom hadrons, and the use of pre-assigned decays.
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Note that pre-assigned decays are decays that are usually specified by
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Monte Carlo event generators. For simplicity, and to avoid dependencies
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on external code, in this test we don't use any MC generator, and we
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pre-assign decays by hand (using the Geant4 decay table: this is done
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in the method SteppingAction::UserSteppingAction). But this does not
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change anything regarding the testing of the pre-assignment mechanism
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of Geant4.
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The set-up is very simple: a cylindrical layer, 2 meter long, whose radii
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(inner and outer) and material can be specified via UI commands. By default,
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the material is Beryllium, with inner radius of 9 mm and outer radius of
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11 mm (i.e. the default thickness is 2 mm). In the rest of the world volume,
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is filled with G4_Galactic material (i.e. very low density gas).
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There is an uniform and constant magnetic field along the z-axis, whose
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value is set via UI command.
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The primary particle, tau- by default, is shot along the x-axis, starting
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from the center (0, 0, 0).
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Its kinetic energy, by default 500 GeV, can be set via UI command.
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All secondaries are killed immediately, so only the primary particle
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is studied.
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The only interesting part of this example is the SteppingAction.
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The decay of the primary particle is pre-assigned there.
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When the primary particle decays, the properties of the decay -
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position, momentum, energy, etc. of the particle at the moment
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of the decay - are collected and then used to:
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- compute the difference between the "MC-truth" decay radius
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(defined as the radius at which the primary would have decayed
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if there were no magnetic field and interactions with matter,
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i.e. no energy loss and no multiple scattering) and the real
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decay radius
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- compute the angular deflection (in degrees) between the initial
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direction of the primary and its final direction at the moment
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it decays
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- the energy loss (i.e. the difference between the initial kinetic energy
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of the primary and the its kinetic energy at the moment of the decay)
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- the energy-momentum violation of the decay (i.e. the difference between
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the sum of the 4-momenta of the decay products and the 4-momentum of
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primary particle at the moment of its decay).
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Some of these information are printed out for each decay, and a summary
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statistics is printed out at the end of the application.
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Look for the string "***LOOKHERE***" for those parameters/options that
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are hardwired in the code (i.e. not available via UI command).
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This example uses the physics list factory, therefore you can specify
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the reference physics list you want to use via the PHYSLIST
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environmental variable (by default, if you don't set it, the FTFP_BERT
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physics list is used).
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To build this example:
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mkdir Build; cd Build
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cmake -DCMAKE_BUILD_TYPE=RelWithDebInfo \
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-DGeant4_DIR=/path-to-geant4-libraries ../.
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make
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To run it:
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./Hadr10 hadr10.in
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which shoots 500 GeV TeV particles - one run of 10'000 events for each
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type of particle - along the x-axis, and print out some information
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regarding their decays, as well as some summary information at the end
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of each run.
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