LHEP Physics List Description

Last modified :

The Geant4 Physics Lists and Builders
Photon Physics
Lepton Physics
Hadron Physics
Ion Physics
Decay Physics

The Geant4 Physics Lists and Builders

The physics lists provided by Geant4 are templated classes based on modular physics lists, that is, they are derived from the G4VModularPhysicsList virtual class. Physics processes and models are grouped into physics constructors which are derived from the G4VPhysicsConstructor virtual class. In the LHEP physics list these constructors are:

Photon Physics

The G4EmStandardPhysics physics constructor assigns three standard electromagnetic physics processes to the gamma:

The G4EmExtraPhysics physics constructor assigns photo-nuclear reactions to the gamma:

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

Lepton Physics

The G4EmStandardPhysics 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 multiple scattering and hadron ionization processes are used for the tau because of its large mass.

For a given particle in the above list, the process ordering reflects the process ordering integers used in the physics list (see code). This ordering is important due to the coupling between multiple scattering and energy loss processes.

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

Caution: Multiple scattering, ionization and bremsstrahlung processes should always be used together, and in the proper order. Removing one or more of them from their assigned particles may cause a crash or at least unpredictable behavior.

The G4EmExtraPhysics constructor assigns electro-nuclear reactions to the electron and positron:

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 Photon Physics.

Muon capture is handled by a hadronic process:

The G4EmExtraPhysics constructor also contains options (both off by default) to include synchrotron radiation for electrons and positrons and muon-nuclear reactions for mu+ and mu-.

Hadron Physics

The physics for hadrons is defined by three constructors, G4EmStandardPhysics, G4HadronElasticPhysics and HadronPhysicsLHEP.

The G4EmStandardPhysics constructor defines the electromagnetic processes for all long-lived charged hadrons:

Note that an ion ionization process is assigned to He3, alphas and generic ions. This process is tuned especially for the larger charge and mass of ions. By contrast, protons, deuterons and tritons are assigned the hadron ionization process.

Hadronic physics models and cross sections must be assigned to the various processes before the processes are assigned to the particles. The following two constructors assign hadronic models to the hadronic processes. In the LHEP physics list, the hadronic cross sections are not explicitly assigned because the default Geant4 hadronic cross sections are used.

The G4HadronElasticPhysics constructor defines elastic scattering for all long-lived hadrons:

For hadron elastic scattering, the same process, G4HadronElasticProcess, is assigned to all the long-lived hadrons. The hadronic model which implements this process is G4LElastic, which has its origins in the GHEISHA model of Geant3. It is used for all incident particle energies.

The HadronPhysicsLHEP constructor defines inelastic processes and models for all long-lived hadrons

For hadron inelastic scattering, each long-lived hadron has its own process. Each of these processes is typically implemented by the combination of two or more models.

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.

Hadronic Models Chosen for this Physics List

The backbone of this, and most, hadronic physics lists consists of the high energy (HEP) and low energy parameterized (LEP) models. They cover all the long-lived particles at all incident energies. LHEP is easily the fastest physics list, but its models are usually not very detailed. Better and slower models exist, but they do not apply to all particles at all energies.

Ion Physics

The G4IonPhysics constructor defines inelastic processes and models for the deuteron, triton and alpha.

Note that no hadronic processes, inelastic or elastic, are assigned to He3 or generic ions.

Decay Physics

The G4DecayPhysics constructor handles the decay channels for all unstable particles defined in the physics list. The same process is assigned to all unstable particles.

Dennis Wright