There are three levels of classes to describe particles in Geant4.
- defines a particle
- describes a particle interacting with materials
- describes a particle traveling in space and time
G4ParticleDefinition aggregates information to
characterize a particle's properties, such as name, mass, spin,
life time, and decay modes.
information to describe the dynamics of particles, such as energy,
momentum, polarization, and proper time, as well as ``particle
G4Track (see Section 5.1) includes all information
necessary for tracking in a detector simulation, such as time,
position, and step, as well as ``dynamic particle''
There are a large number of elementary particles and nuclei. Geant4
G4ParticleDefinition class to represent
particles, and various particles, such as the electron, proton, and
gamma have their own classes derived from
We do not need to make a class in Geant4 for every kind of particle in the world. There are more than 100 types of particles defined in Geant4 by default. Which particles should be included, and how to implement them, is determined according to the following criteria. (Of course, the user can define any particles he wants. Please see the User's Guide: For ToolKit Developers).
This list includes all particles in Geant4 and you can see properties of particles such as
- PDG encoding
- mass and width
- electric charge
- spin, isospin and parity
- magnetic moment
- quark contents
- life time and decay modes
Here is a list of particles in Geant4. This list is generated automatically by using Geant4 functionality, so listed values are same as those in your Geant4 application (as far as you do not change source codes).
elementary particles which should be tracked in Geant4 volumes
All particles that can fly a finite length and interact with materials in detectors are included in this category. In addition, some particles with a very short lifetime are included for user's convenience.
Stable means that the particle can not decay, or has a very small possibility to decay in detectors, e.g., gamma, electron, proton, and neutron.
long life (>10-14sec) particles
Particles which may travel a finite length, e.g., muon, charged pions.
short life particles that decay immediately in Geant4
For example, pi0, eta
K0 "decays" immediately into K0S or K0L, and then K0S/ K0L decays according to its life time and decay modes.
Gamma and optical photon are distinguished in the simulation view, though both are the same particle (photons with different energies). For example, optical photon is used for Cerenkov light and scintillation light.
Geantino and charged geantino are virtual particles for simulation which do not interact with materials and undertake transportation processes only.
Any kinds of nucleus can be used in Geant4, such as alpha(He-4), uranium-238 and excited states of carbon-14. In addition, Geant4 provides hyper-nuclei. Nuclei in Geant4 are divided into two groups from the viewpoint of implementation.
Light nuclei frequently used in simulation, e.g., alpha, deuteron, He3, triton.
heavy nuclei (including hyper-nuclei)
Nuclei other than those defined in the previous category.
Light anti-nuclei for example anti-alpha.
Note that G4ParticleDefinition represents nucleus state and G4DynamicParticle represents atomic state with some nucleus. Both alpha particle with charge of +2e and helium atom with no charge aggregates the same "particle definition" of G4Alpha, but different G4DynamicParticle objects should be assigned to them. (Details can be found below)
Particles with very short life time decay immediately and are never tracked in the detector geometry. These particles are usually used only inside physics processes to implement some models of interactions.
G4VShortLivedParticleis provided as the base class for these particles. All classes related to particles in this category can be found in
shortlivedsub-directory under the
- quarks/di-quarks: For example, all 6 quarks.
- baryon excited states with very short life: For example, spin 3/2 baryons and anti-baryons
- meson excited states with very short life: For example, spin 1 vector bosons
Single object created in the initialization : Categories a, b-1
These particles are frequently used for tracking in Geant4. An individual class is defined for each particle in these categories. The object in each class is unique. The user can get pointers to these objects by using static methods in their own classes. The unique object for each class is created when its static method is called in the ``initialization phase''.
On-the-fly creation: Category b-2
Ions will travel in a detector geometry and should
be tracked, however, the number of ions which may be used for
hadronic processes is so huge that ions are dynamically
created by requests from processes (and users).
Each ion corresponds to one object of the
G4IonTable class is a dictionary for ions.
G4IonTable::GetIon() method to create ions
on the fly. (
G4IonTable::FIndIon() method returns
pointer to the specified ion. If the ion does not exists, it returns
zero without creating any ion.
G4NucleiPropertiesTableAME03 contains a table of
mesaured mass values of about 3100 stable nuclei (ground states).
mass values of about 8000 nuclei (ground states).
G4IsotopeTable describes properties of ions
(exited energy, decay modes, life time and magnetic moments),
which are used to create ions.
G4NuclideTable is provided as a list of nuclei in Geant4.
It contains about 2900 ground states and 4000 excited states.
Users can register his/her
G4IsotopeTable to the
Processes attached to heavy ions are same as those for
G4GenericIon class. In other words, you need to
G4GenericIon and attach processes to it
if you want to use heavy ions.
G4ParticleGun can shoot any heavy ions
with /gun/ions command after ``ion'' is selected by /gun/particle command.
Dynamic creation by processes: Category c
Particle types in this category are are not created
by default, but will only be created by request from processes or
directly by users. Each shortlived particle corresponds to one
object of a class derived from
and it will be created dynamically during the ``initialization
G4ParticleDefinition class has ``read-only'' properties
to characterize individual particles, such as name, mass, charge,
spin, and so on. These properties are set during initialization of
each particle. Methods to get these properties are listed in
||magnetic moment (0: not defined or no magnetic moment)|
||parity (0:not defined)|
||charge conjugation (0:not defined)|
||3rd-component of iso-spin|
||G-parity (0:not defined)|
||particle encoding number by PDG|
||encoding for anti-particle of this particle|
Table 5.2. Methods to get particle properties.
Table 5.3 shows the methods of
getting information about decay modes and the life time of the
Table 5.3. Methods to get particle decay modes and life time.
Users can modify these properties, though the other properties listed above can not be change without rebuilding the libraries.
Each particle has its own
object that manages a list of processes applicable to the
particle.(see Section 2.5.2 )
G4DynamicParticle class has kinematics information for
the particle and is used for describing the dynamics of physics
processes. The properties in
G4DynamicParticle are listed in
||normalized momentum vector|
||definition of particle|
||dynamical spin (i.e. total angular momentum as a ion/atom )|
||dynamical magnetic moment (i.e. total magnetic moment as a ion/atom )|
||dynamical electric charge (i.e. total electric charge as a ion/atom )|
||electron orbits for ions|
Table 5.4. Methods to set/get values.
Here, the dynamical mass is defined as the mass for the dynamic
particle. For most cases, it is same as the mass defined in
G4ParticleDefinition class ( i.e. mass value given by
GetPDGMass() method). However, there are two
- resonance particle
Resonance particles have large mass width and the total energy of decay products at the center of mass system can be different event by event.
As for ions,
G4ParticleDefintion defines a nucleus and
G4DynamicParticle defines an atom.
G4ElectronOccupancy describes state of orbital electrons.
So, the dynamic mass can be different from the PDG mass by the mass
of electrons (and their binding energy). In addition, the dynamical
charge, spin and magnetic moment are those of the atom/ion
(i.e. including nucleus and orbit electrons).
Decay products of heavy flavor particles are given in many event
generators. In such cases,
G4VPrimaryGenerator sets this
*thePreAssignedDecayProducts. In addition,
decay time of the particle can be set arbitrarily time by using