Shielding Physics List Description

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Modular Physics Lists
Boson Physics
Lepton Physics
Hadron Physics
Meson Physics
Nucleon Physics
Hyperon Physics
AntiBaryon Physics
Ion Physics

Modular Physics List and Physics Constructors

The shielding physics list contains the best-guess selection of electromagnetic and hadronic physics processes required to run a shielding, high energy or underground detector simulation. The processes and models are organized using a modular physics list and a set of physics constructors (builders) which allow related physics processes, models and particles to be grouped together.

Boson Physics

The boson physics constructor defines the gamma and two fictitious particles, the Geantino and the ChargedGeantino.

Four processes are assigned to the gamma:

The Geantino is a chargeless, massless, completely non-interacting particle which can be used for geometry and tracking diagnostics. The ChargedGeantino is also massless and non-interacting, but has a charge so that it can be tracked properly in a magnetic field. Aside from the transportation process, neither of these particles can be assigned an interaction process.

Two hadronic models are required to describe photon interactions with nuclei and nucleons. Hadronic models are discussed further in Hadron Physics.

Lepton Physics

The lepton physics constructor defines electrons, muons and taus along with their corresponding neutrinos. The following processes are assigned to each particle:

Note that the ionization and bremsstrahlung processes for e+/e- are different from those for mu+/mu-. They are specially tuned for the mass difference and other effects. The hadron ionization process is used for the tau because of its large mass.

One hadronic model is required to describe electron- and positron-induced nuclear reactions. The electro-nuclear reaction model relies on the method of equivalent photons to calculate a virtual photon spectrum, which in turn is interacted with the nucleus and nucleons using a photo-nuclear model similar to that in Boson Physics.

No processes, except transportation, currently exist for the neutrinos.

Hadron Physics

The hadron physics constructor defines all stable and long-lived baryons, and all long-lived mesons. These are the particles that Geant4 can track and therefore require processes to be assigned. Short-lived particles are not tracked, but they appear in some hadronic models, so a large list of resonances, quarks and diquarks is also defined.

Both electromagnetic and hadronic processes are assigned to the long-lived hadrons. For the hadronic processes an extra level of detail must be addressed. Cross sections and physics models must be assigned to the various processes before the processes are assigned to the particles.

For hadron elastic scattering, the same process, G4WHadronElasticProcess, is assigned to almost all the long-lived hadrons.

Meson Physics

Nucleon Physics

Hyperon Physics

AntiBaryon Physics

Ion Physics


Dennis Wright