source: trunk/documents/UserDoc/DocBookUsersGuides/ForApplicationDeveloper/xml/TrackingAndPhysics/particle.xml@ 1330

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<!--    Changed by: Katsuya Amako, 21-Sep-1998                -->
<!--    Proof read by: Joe Chuma,  29-Jun-1999                -->
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<!-- ******************* Section (Level#1) ****************** -->
<sect1 id="sect.Parti">
<title>
Particles
</title>


<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.Parti.Basic">
<title>
Basic concepts
</title>

<para>
There are three levels of classes to describe particles in Geant4.

<variablelist>
  <varlistentry>
    <term>
      <emphasis>G4ParticleDefinition</emphasis>
    </term>
    <listitem>
      defines a particle
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis>G4DynamicParticle</emphasis>
    </term>
    <listitem>
      describes a particle interacting with materials
    </listitem>
  </varlistentry>
  <varlistentry>
    <term>
      <emphasis>G4Track</emphasis>
    </term>
    <listitem>
      describes a particle traveling in space and time
    </listitem>
  </varlistentry>
</variablelist>
</para>

<para>
<emphasis>G4ParticleDefinition</emphasis> aggregates information to
characterize a particle's properties, such as name, mass, spin,
life time, and decay modes. <emphasis>G4DynamicParticle</emphasis> aggregates
information to describe the dynamics of particles, such as energy,
momentum, polarization, and proper time, as well as ``particle
definition'' information. <emphasis>G4Track</emphasis> includes all information
necessary for tracking in a detector simulation, such as time,
position, and step, as well as ``dynamic particle''
information.
</para>

<para>
<emphasis>G4Track</emphasis> has all the information necessary for tracking in
Geant4. It includes position, time, and step, as well as
kinematics. Details of <emphasis>G4Track</emphasis> will be described in 
<xref linkend="sect.Track" />.
</para>

</sect2>


<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.Parti.Def">
<title>
Definition of a particle
</title>

<para>
There are a large number of elementary particles and nuclei. Geant4
provides the <emphasis>G4ParticleDefinition</emphasis> class to represent
particles, and various particles, such as the electron, proton, and
gamma have their own classes derived from
<emphasis>G4ParticleDefinition</emphasis>.
</para>

<para>
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 <emphasis role="bold">User's Guide: For ToolKit
Developers</emphasis>).
</para>


<!-- ******************* Section (Level#3) ****************** -->
<sect3 id="sect.Parti.Def.PartiList">
<title>
Particle List in Geant4
</title>

<para>
This list includes all particles in Geant4 and you can see
properties of particles such as

<itemizedlist spacing="compact">
  <listitem><para>
    PDG encoding
  </para></listitem>
  <listitem><para>
    mass and width
  </para></listitem>
  <listitem><para>
    electric charge
  </para></listitem>
  <listitem><para>
    spin, isospin and parity
  </para></listitem>
  <listitem><para>
    magnetic moment
  </para></listitem>
  <listitem><para>
    quark contents
  </para></listitem>
 <listitem><para>
    life time and decay modes
  </para></listitem>
</itemizedlist>
</para>

<para>
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).
</para>

<!-- ******* Bridgehead ******* -->
<bridgehead renderas='sect4'>
Categories
</bridgehead>

<para>
<itemizedlist spacing="compact">
  <listitem><para>
    <ulink url="./AllResources/TrackingAndPhysics/particleList.src/quarks/index.html">
    gluon / quarks / di-quarks
    </ulink>
  </para></listitem>
  <listitem><para>
    <ulink url="./AllResources/TrackingAndPhysics/particleList.src/leptons/index.html">
    leptons
    </ulink>
  </para></listitem>
  <listitem><para>
    <ulink url="./AllResources/TrackingAndPhysics/particleList.src/mesons/index.html">
    mesons
    </ulink>
  </para></listitem>
  <listitem><para>
    <ulink url="./AllResources/TrackingAndPhysics/particleList.src/baryons/index.html">
    baryons
    </ulink>
  </para></listitem>
  <listitem><para>
    <ulink url="./AllResources/TrackingAndPhysics/particleList.src/ions/index.html">
    ions
    </ulink>
  </para></listitem>
  <listitem><para>
    <ulink url="./AllResources/TrackingAndPhysics/particleList.src/others/index.html">
    others
    </ulink>
  </para></listitem>
</itemizedlist>
</para>

</sect3>

<!-- ******************* Section (Level#3) ****************** -->
<sect3 id="sect.Parti.Def.Classif">
<title>
Classification of particles
</title>

<para>
<orderedlist spacing="compact">
  <listitem><para>
    <para>
    elementary particles which should be tracked in Geant4 volumes
    </para>
    <para>
    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.

    <orderedlist spacing="compact">
      <listitem><para>
        stable particles
        <para>
        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.
        </para>
      </para></listitem>
      <listitem><para>
        long life (&gt;10<superscript>-14</superscript>sec) particles
        <para>
        Particles which may travel a finite length, e.g., muon, charged
        pions.
        </para>
      </para></listitem>
      <listitem><para>
        short life particles that decay immediately in Geant4
        <para>
        For example, pi<superscript>0</superscript>, eta
        </para>
      </para></listitem>
      <listitem><para>
        K<superscript>0</superscript> system
        <para>
        K<superscript>0</superscript> "decays" immediately into 
        K<superscript>0</superscript><subscript>S</subscript>
        or K<superscript>0</superscript><subscript>L</subscript>, and then
        K<superscript>0</superscript><subscript>S</subscript>/
        K<superscript>0</superscript><subscript>L</subscript> decays
        according to its life time and decay modes.
        </para>
      </para></listitem>
      <listitem><para>
        optical photon
        <para>
        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.
        </para>
      </para></listitem>
      <listitem><para>
        geantino/charged geantino
        <para>
        Geantino and charged geantino are virtual particles for
        simulation which do not interact with materials and undertake
        transportation processes only.
        </para>
      </para></listitem>
    </orderedlist>
    </para>
  </para></listitem>
  <listitem><para>
    nuclei
    <para>
    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.
    <orderedlist spacing="compact">
      <listitem><para>
        light nuclei
        <para>
        Light nuclei frequently used in simulation, e.g., alpha, deuteron,
        He3, triton.
        </para>
      </para></listitem>
      <listitem><para>
        heavy nuclei (including hyper-nuclei)
        <para>
        Nuclei other than those defined in the previous category.
        </para>
      </para></listitem>
    </orderedlist>

    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)
    </para>
  </para></listitem>
  <listitem><para>
    short-lived particles
    <para>
    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. <emphasis>G4VShortLivedParticle</emphasis> is provided as 
    the base class for these particles. All classes related to particles in 
    this category can be found in <literal>shortlived</literal> sub-directory 
    under the <literal>particles</literal> directory.

    <orderedlist spacing="compact">
      <listitem><para>
        quarks/di-quarks
        <para>
        For example, all 6 quarks.
        </para>
      </para></listitem>
      <listitem><para>
        gluon
      </para></listitem>
      <listitem><para>
        baryon excited states with very short life
        <para>
        For example, spin 3/2 baryons and anti-baryons
        </para>
      </para></listitem>
      <listitem><para>
        meson excited states with very short life
        <para>
        For example, spin 1 vector bosons
        </para>
      </para></listitem>
    </orderedlist>
    </para>
  </para></listitem>
</orderedlist>
</para>

</sect3>


<!-- ******************* Section (Level#3) ****************** -->
<sect3 id="sect.Parti.Def.Imple">
<title>
Implementation of particles
</title>

<para>
<emphasis>Single object created in the initialization :</emphasis> 
Categories a, b-1
</para>

<para>
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''.
</para>

<para>
<emphasis>On-the-fly creation:</emphasis> Category b-2
</para>

<para>
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 <emphasis>G4Ions</emphasis>
class.
<emphasis>G4IonTable</emphasis> class is a dictionary for ions. 
<literal>G4ParticleTable::GetIon()</literal> method invokes
<literal>G4IonTable::GetIon()</literal> method to create ions 
on the fly. 
</para>

<para>
 Users can register a <emphasis>G4IsotopeTable</emphasis> to the
<emphasis>G4IonTable</emphasis>. <emphasis>G4IsotopeTable</emphasis>
describes properties of ions (exited energy, decay modes, life time
and magnetic moments), which are used to create ions.
</para>

<para>
Processes attached to heavy ions are same as those for
<emphasis>G4GenericIon</emphasis> class. In other words, you need to
create <emphasis>G4GenericIon</emphasis> and attach processes to it 
if you want to use heavy ions. 
</para>

<para>
<emphasis>G4ParticleGun</emphasis> can shoot any heavy ions 
with /gun/ions command after ``ion'' is selected by /gun/particle command.
</para>

<para>
<emphasis>Dynamic creation by processes:</emphasis> Category c
</para>

<para>
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 <emphasis>G4VshortLivedParticle</emphasis>, 
and it will be created dynamically during the ``initialization
phase''.
</para>

</sect3>


<!-- ******************* Section (Level#3) ****************** -->
<sect3 id="sect.Parti.Def.G4Parti">
<title>
G4ParticleDefinition
</title>

<para>
The <emphasis>G4ParticleDefinition</emphasis> 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 
<xref linkend="table.Parti_1" />.

<table id="table.Parti_1">
<title>
Methods to get particle properties.
</title>

<tgroup cols="2">
  <tbody>
  <row>
    <entry>
      <literal>G4String GetParticleName()</literal>
    </entry>
    <entry>
      particle name
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double GetPDGMass()</literal>
    </entry>
    <entry>
      mass
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double GetPDGWidth()</literal>
    </entry>
    <entry>
      decay width
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double GetPDGCharge()</literal>
    </entry>
    <entry>
      electric charge
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double GetPDGSpin()</literal>
    </entry>
    <entry>
      spin
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double GetPDGMagneticMoment()</literal>
    </entry>
    <entry>
      magnetic moment (0: not defined or no magnetic moment)
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4int GetPDGiParity()</literal>
    </entry>
    <entry>
      parity (0:not defined)
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4int GetPDGiConjugation()</literal>
    </entry>
    <entry>
      charge conjugation (0:not defined)
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double GetPDGIsospin()</literal>
    </entry>
    <entry>
      iso-spin
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double GetPDGIsospin3()</literal>
    </entry>
    <entry>
      3<superscript>rd</superscript>-component of iso-spin
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4int GetPDGiGParity()</literal>
    </entry>
    <entry>
      G-parity (0:not defined)
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4String GetParticleType()</literal>
    </entry>
    <entry>
      particle type
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4String GetParticleSubType()</literal>
    </entry>
    <entry>
      particle sub-type
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4int GetLeptonNumber()</literal>
    </entry>
    <entry>
      lepton number
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4int GetBaryonNumber()</literal>
    </entry>
    <entry>
      baryon number
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4int GetPDGEncoding()</literal>
    </entry>
    <entry>
      particle encoding number by PDG
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4int GetAntiPDGEncoding()</literal>
    </entry>
    <entry>
      encoding for anti-particle of this particle
    </entry>
  </row>
  </tbody>
</tgroup>
</table>
</para>

<para>
<xref linkend="table.Parti_2" /> shows the methods of 
<emphasis>G4ParticleDefinition</emphasis> for
getting information about decay modes and the life time of the
particle.

<table id="table.Parti_2">
<title>
Methods to get particle decay modes and life time.
</title>

<tgroup cols="2">
  <tbody>
  <row>
    <entry>
      <literal>G4bool GetPDGStable()</literal>
    </entry>
    <entry>
      stable flag
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double GetPDGLifeTime()</literal>
    </entry>
    <entry>
      life time
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4DecayTable* GetDecayTable()</literal>
    </entry>
    <entry>
      decay table
    </entry>
  </row>
  </tbody>
</tgroup>
</table>
</para>

<para>
Users can modify these properties, though the other properties
listed above can not be change without rebuilding the
libraries.
</para>

<para>
Each particle has its own <emphasis>G4ProcessManger</emphasis>
object that manages a list of processes applicable to the
particle.(see <xref linkend="sect.HowToSpecPhysProc.ManagingProc"/> )
</para>


</sect3>
</sect2>


<!-- ******************* Section (Level#2) ****************** -->
<sect2 id="sect.Parti.Dynam">
<title>
Dynamic particle
</title>

<para>
The <emphasis>G4DynamicParticle</emphasis> class has kinematics information for
the particle and is used for describing the dynamics of physics
processes. The properties in <emphasis>G4DynamicParticle</emphasis> are listed in
<xref linkend="table.Parti_4" />.

<table id="table.Parti_4">
<title>
Methods to set/get cut off values.
</title>

<tgroup cols="2">
  <tbody>
  <row>
    <entry>
      <literal>G4double theDynamicalMass</literal>
    </entry>
    <entry>
      dynamical mass
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4ThreeVector theMomentumDirection</literal>
    </entry>
    <entry>
      normalized momentum vector
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4ParticleDefinition* theParticleDefinition</literal>
    </entry>
    <entry>
      definition of particle
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double theDynamicalSpin</literal>
    </entry>
    <entry>
      dynamical spin 
      (i.e. total angular momentum as a ion/atom )
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4ThreeVector thePolarization</literal>
    </entry>
    <entry>
      polarization vector
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double theMagneticMoment</literal>
    </entry>
    <entry>
      dynamical magnetic moment
      (i.e. total magnetic moment as a ion/atom )
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double theKineticEnergy</literal>
    </entry>
    <entry>
      kinetic energy
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double theProperTime</literal>
    </entry>
    <entry>
      proper time
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4double theDynamicalCharge</literal>
    </entry>
    <entry>
      dynamical electric charge 
      (i.e. total electric charge as a ion/atom )
    </entry>
  </row>
  <row>
    <entry>
      <literal>G4ElectronOccupancy* theElectronOccupancy</literal>
    </entry>
    <entry>
      electron orbits for ions
    </entry>
  </row>
  </tbody>
</tgroup>
</table>
</para>

<para>
Here, the dynamical mass is defined as the mass for the dynamic
particle. For most cases, it is same as the mass defined in
<emphasis>G4ParticleDefinition</emphasis> class ( i.e. mass value given by
<literal>GetPDGMass()</literal> method). However, there are two
exceptions.

<itemizedlist spacing="compact">
  <listitem><para>
    resonance particle
  </para></listitem>
  <listitem><para>
    ions
  </para></listitem>
</itemizedlist>
</para>

<para>
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.
</para>

<para>
As for ions, <emphasis>G4ParticleDefintion</emphasis> defines a nucleus and
<emphasis>G4DynamicParticle</emphasis> defines an atom.
<emphasis>G4ElectronOccupancy</emphasis> 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). 
</para>

<para>
Decay products of heavy flavor particles are given in many event
generators. In such cases, <emphasis>G4VPrimaryGenerator</emphasis> sets this
information in <literal>*thePreAssignedDecayProducts</literal>. In addition,
decay time of the particle can be set arbitrarily time by using
<literal>PreAssignedDecayProperTime</literal>.
</para>


</sect2>
</sect1>