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| 2 | <TITLE>
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| 3 | </TITLE>
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| 4 | <!-- Changed by: Katsuya Amako, 21-Sep-1998 -->
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| 5 | <!-- Proof read by: Joe Chuma, 29-Jun-1999 -->
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| 6 | <!-- Changed by: Hisaya Kurashige, 28-Oct-2001 -->
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| 7 | <!-- Changed by: Dennis Wright, 27-Nov-2001 -->
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| 8 | <!-- Changed by: Dennis Wright, 18-Jan-2006 -->
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| 9 |
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| 10 | <BODY>
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| 11 | <TABLE WIDTH="100%"><TR>
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| 12 | <TD>
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| 13 |
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| 14 |
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| 15 | <A HREF="index.html">
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| 16 | <IMG SRC="../../../../resources/html/IconsGIF/Contents.gif" ALT="Contents"></A>
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| 17 | <A HREF="physicsProcess.html">
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| 18 | <IMG SRC="../../../../resources/html/IconsGIF/Previous.gif" ALT="Previous"></A>
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| 19 | <A HREF="thresholdVScut.html">
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| 20 | <IMG SRC="../../../../resources/html/IconsGIF/Next.gif" ALT="Next"></A>
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| 21 | </TD>
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| 22 | <TD ALIGN="Right">
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| 23 | <FONT SIZE="-1" COLOR="#238E23">
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| 24 | <B>Geant4 User's Guide</B>
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| 25 | <BR>
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| 26 | <B>For Application Developers</B>
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| 27 | <BR>
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| 28 | <B>Tracking and Physics</B>
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| 29 | </FONT>
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| 30 | </TD>
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| 31 | </TR></TABLE>
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| 32 | <BR><BR>
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| 33 |
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| 34 | <P ALIGN="Center">
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| 35 | <FONT SIZE="+3" COLOR="#238E23">
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| 36 | <B>5.3 Particles</B>
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| 37 | </FONT>
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| 38 | <BR><BR>
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| 39 |
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| 40 | <HR ALIGN="Center" SIZE="7%">
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| 41 | <p>
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| 42 |
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| 43 | <a name="5.3.1">
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| 44 | <H2>5.3.1 Basic concepts</H2></a>
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| 45 |
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| 46 | There are three levels of classes to describe particles in Geant4.
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| 47 | <p>
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| 48 | <table>
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| 49 | <tr>
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| 50 | <td><i>G4ParticleDefinition</i>
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| 51 | <td>defines a particle
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| 52 | <tr>
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| 53 | <td><i>G4DynamicParticle</i>
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| 54 | <td>describes a particle interacting with materials
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| 55 | <tr>
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| 56 | <td><i>G4Track</i>
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| 57 | <td>describes a particle traveling in space and time
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| 58 | </table>
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| 59 | <p>
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| 60 | <i>G4ParticleDefinition</i> aggregates information to characterize
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| 61 | a particle's properties, such as name, mass, spin, life time, and decay modes.
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| 62 | <i>G4DynamicParticle</i> aggregates information to describe the dynamics of
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| 63 | particles, such as energy, momentum, polarization, and proper time,
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| 64 | as well as ``particle definition'' information.
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| 65 | <i>G4Track</i> includes all information necessary for tracking
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| 66 | in a detector simulation, such as time, position, and step,
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| 67 | as well as ``dynamic particle'' information.
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| 68 | <P>
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| 69 | <i>G4Track</i> has all the information necessary for tracking in Geant4.
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| 70 | It includes position, time, and step, as well as kinematics.
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| 71 | Details of <i>G4Track</i> will be described in
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| 72 | <a href="tracking.html">Section 5.1</a>.
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| 73 | <P>
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| 74 | Besides above three classes, <i>G4ParticleWithCuts</i> class plays
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| 75 | an important role. It provides the functionality to convert
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| 76 | the cut value in range into energy thresholds for all materials.
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| 77 | <HR>
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| 78 | <a name="5.3.2">
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| 79 | <H2>5.3.2 Definition of a particle</H2></a>
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| 80 |
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| 81 | There are a large number of elementary particles and nuclei. Geant4 provides the
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| 82 | <i>G4ParticleDefinition</i> class to represent particles, and various particles,
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| 83 | such as the electron, proton, and gamma have their own classes derived from
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| 84 | <i>G4ParticleDefinition</i>.
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| 85 | <p>
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| 86 | We do not need to make a class in Geant4 for every kind of particle in the world.
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| 87 | There are more than 100 types of particles defined in Geant4 by default.
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| 88 | Which particles should be included, and how to
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| 89 | implement them, is determined according to the following criteria.
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| 90 | (Of course, the user can define any particles he wants. Please see the
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| 91 | <b>User's Guide: For ToolKit Developers</b>)
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| 92 | <P>
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| 93 | <BR>
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| 94 |
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| 95 | <H4>5.3.2.1 Particle List in Geant4</H4>
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| 96 | This list includes all particles in Geant4 and you can see
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| 97 | properties of particles such as
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| 98 | <UL>
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| 99 | <LI> PDG encoding
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| 100 | <LI> mass and width
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| 101 | <LI> spin, isospin and parity
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| 102 | <LI> life time and decay modes
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| 103 | <LI> quark contents
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| 104 | </UL>
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| 105 | Here is a list of particles in Geant4. This list is generated automatically
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| 106 | by using Geant4 functionality,
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| 107 | so listed values are same as those in your Geant4 application.
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| 108 | (as far as you do not change source codes)
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| 109 | <P>
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| 110 | <H5> Categories </H5>
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| 111 | <UL>
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| 112 | <LI><A HREF="../Appendix/particleList.src/quarks/index.html">gluon / quarks / di-quarks </A></TD>
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| 113 | <LI><A HREF="../Appendix/particleList.src/leptons/index.html">leptons</A></TD>
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| 114 | <LI><A HREF="../Appendix/particleList.src/mesons/index.html">mesons</A></TD>
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| 115 | <LI><A HREF="../Appendix/particleList.src/baryons/index.html">baryons</A></TD>
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| 116 | <LI><A HREF="../Appendix/particleList.src/ions/index.html">ions</A></TD>
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| 117 | <LI><A HREF="../Appendix/particleList.src/others/index.html">others</A></TD>
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| 118 | </UL>
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| 119 |
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| 120 | <H4>5.3.2.2 Classification of particles</H4>
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| 121 |
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| 122 | <ol type=a>
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| 123 | <li>elementary particles which should be tracked in Geant4<BR>
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| 124 | All particles that can fly a finite length and interact with
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| 125 | materials in detectors are included in this category.
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| 126 | In addition, some particles with a very short lifetime are included.
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| 127 | <ol type=1>
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| 128 | <li>stable particles<BR>
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| 129 | Stable means that the particle can not decay,
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| 130 | or has a very small possibility to decay in detectors,
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| 131 | e.g., gamma, electron, proton, and neutron.
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| 132 | <li>long life (>10<sup>-14</sup>sec) particles<BR>
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| 133 | Particles which may travel a finite length, e.g., muon, charged pions.
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| 134 | <li>short life particles that need to decay in Geant4<BR>
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| 135 | For example, <font face="symbol">p</font><sup>0</sup>,<font face="symbol">h</font>
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| 136 | <li>K<sup>0</sup> system<BR>
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| 137 | K<sup>0</sup> "decays" immediately into K<sup>0</sup><sub>S</sub> or
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| 138 | K<sup>0</sup><sub>L</sub>,
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| 139 | and then K<sup>0</sup><sub>S</sub>/K<sup>0</sup><sub>L</sub> decays
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| 140 | according to its life time and decay modes.
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| 141 | <li>optical photons<BR>
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| 142 | Gammas and optical photons are distinguished in the simulation view,
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| 143 | though both are the same particle (photons with different energies).
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| 144 | For example, optical photons are used for Cerenkov light and scintillation light.
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| 145 | <li>geantinos/charged geantinos<BR>
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| 146 | Geantinos and charged geantinos are virtual particles for simulation
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| 147 | which do not interact with materials and undertake transportation processes only.
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| 148 | </ol>
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| 149 | <li>nuclei<BR>
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| 150 | Any kinds of nucleus can be used in Geant4, such as alpha(He-4), uranium-238 and
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| 151 | excited states of carbon-14. Nuclei in Geant4 are divided into two groups from
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| 152 | the viewpoint of implementation.
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| 153 | <ol type=1>
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| 154 | <li>light nuclei<BR>
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| 155 | Light nuclei frequently used in simulation, e.g.,
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| 156 | alpha, deuteron, He3, triton.
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| 157 | <li>heavy nuclei<BR>
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| 158 | Nuclei other than those defined in the previous category.
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| 159 | </ol>
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| 160 | Note that G4ParticleDefinition represents nucleus state and G4DynamicParticle
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| 161 | represents atomic state with some nucleus. Both alpha particle with charge of +2
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| 162 | and helium atom with no charge aggregates the same "particle definition" of G4Alpha,
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| 163 | but different G4DynamicParticle objects should be assigned to them.
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| 164 | (Details can be found below)
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| 165 | <li>short-lived particles<BR>
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| 166 | Particles with very short life time decay immediately and are never tracked
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| 167 | in the detector geometry. These particles are usually used only inside
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| 168 | physics processes to implement some models of interactions.
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| 169 | <i>G4VShortLivedParticle</i> is provided as the base class for these particles.
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| 170 | All classes related to particles in this category
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| 171 | can be found in <tt>shortlived</tt> sub-directory under the
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| 172 | <tt>particles</tt> directory.
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| 173 | <ol type=1>
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| 174 | <li>quarks/di-quarks<BR>
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| 175 | For example, all 6 quarks.
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| 176 | <li>gluons<BR>
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| 177 | <li>baryon excited states with very short life<BR>
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| 178 | For example, spin 3/2 baryons and anti-baryons
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| 179 | <li>meson excited states with very short life<BR>
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| 180 | For example, spin 1 vector bosons
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| 181 | </ol>
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| 182 | </ol>
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| 183 | <P>
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| 184 |
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| 185 | <H4>5.3.2.3 Implementation of particles</H4>
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| 186 |
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| 187 | <table>
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| 188 |
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| 189 | <tr>
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| 190 | <td>Dynamic creation by user's physics list:
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| 191 | <td>Categories a, b-1
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| 192 | <tr>
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| 193 | <td colspan=2>These particles are frequently used for tracking in Geant4.
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| 194 | An individual class is defined for each particle in these categories.
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| 195 | The object in each class should be created in the physics list and should be unique.
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| 196 | The user can get pointers to these objects by using static methods in their own classes.
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| 197 | <p>
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| 198 | WARNING: Beginning with Geant4 version 8.0, all particle definitions are revised to "non-static" objects.
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| 199 | <tr><td><td>
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| 200 | <tr><td><td>
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| 201 | <tr>
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| 202 | <td>On-the-fly creation:
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| 203 | <td>Category b-2
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| 204 | <tr>
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| 205 | <td colspan=2>Ions will travel in a detector geometry and should be tracked,
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| 206 | however, the number of ions which may be used for hadronic processes is so huge
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| 207 | that ions are dynamic rather than static. Each ion corresponds to one object of the
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| 208 | <i>G4Ions</i> class, and it will be created on the fly in the <tt>G4ParticleTable::GetIon()</tt>
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| 209 | method.
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| 210 | <tr><td><td>
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| 211 | <tr><td><td>
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| 212 | <tr>
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| 213 | <td>: <td>Category c
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| 214 | <tr>
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| 215 | <td colspan=2>Particle types in this category are are not created by default,
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| 216 | but will only be created by request from processes or directly by users.
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| 217 | Each shortlived particle corresponds to one object of a class derived from
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| 218 | <i>G4VshortLivedParticle</i>, and it will be created dynamically during
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| 219 | the ``initialization phase''.
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| 220 |
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| 221 | </table>
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| 222 |
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| 223 | <P>
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| 224 |
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| 225 | <H4>5.3.2.4 <i>G4ParticleDefinition</i></H4>
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| 226 |
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| 227 | The <i>G4ParticleDefinition</i> class has ``read-only'' properties to characterize individual
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| 228 | particles, such as name, mass, charge, spin, and so on. These properties are set during
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| 229 | initialization of each particle. Methods to get these properties are listed in Table 5.3.1.
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| 230 | <p>
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| 231 | <center><table border=2 cellpadding=10>
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| 232 | <tr>
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| 233 | <td><tt>G4String GetParticleName()</tt>
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| 234 | <td>particle name
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| 235 | <tr>
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| 236 | <td><tt>G4double GetPDGMass()</tt>
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| 237 | <td>mass
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| 238 | <tr>
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| 239 | <td><tt>G4double GetPDGWidth()</tt>
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| 240 | <td>decay width
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| 241 | <tr>
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| 242 | <td><tt>G4double GetPDGCharge()</tt>
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| 243 | <td>electric charge
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| 244 | <tr>
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| 245 | <td><tt>G4double GetPDGSpin()</tt>
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| 246 | <td>spin
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| 247 | <tr>
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| 248 | <td><tt>G4int GetPDGiParity()</tt>
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| 249 | <td>parity (0:not defined)
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| 250 | <tr>
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| 251 | <td><tt>G4int GetPDGiConjugation()</tt>
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| 252 | <td>charge conjugation (0:not defined)
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| 253 | <tr>
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| 254 | <td><tt>G4double GetPDGIsospin()</tt>
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| 255 | <td>iso-spin
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| 256 | <tr>
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| 257 | <td><tt>G4double GetPDGIsospin3()</tt>
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| 258 | <td>3<sup>rd</sup>-component of iso-spin
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| 259 | <tr>
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| 260 | <td><tt>G4int GetPDGiGParity()</tt>
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| 261 | <td>G-parity (0:not defined)
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| 262 | <tr>
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| 263 | <td><tt>G4String GetParticleType()</tt>
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| 264 | <td>particle type
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| 265 | <tr>
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| 266 | <td><tt>G4String GetParticleSubType()</tt>
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| 267 | <td>particle sub-type
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| 268 | <tr>
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| 269 | <td><tt>G4int GetLeptonNumber()</tt>
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| 270 | <td>lepton number
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| 271 | <tr>
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| 272 | <td><tt>G4int GetBaryonNumber()</tt>
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| 273 | <td>baryon number
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| 274 | <tr>
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| 275 | <td><tt>G4int GetPDGEncoding()</tt>
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| 276 | <td>particle encoding number by PDG
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| 277 | <tr>
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| 278 | <td><tt>G4int GetAntiPDGEncoding()</tt>
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| 279 | <td>encoding for anti-particle of this particle
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| 280 | <tr>
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| 281 | <td align=center colspan=2>
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| 282 | Table 5.3.1<BR>
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| 283 | Methods to get particle properties.
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| 284 | </td>
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| 285 | </tr>
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| 286 | </table></center>
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| 287 | <P>
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| 288 | Table 5.3.2 shows the methods of <i>G4ParticleDefinition</i> for getting information about decay modes
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| 289 | and the life time of the particle.
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| 290 | <p>
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| 291 | <center><table border=2 cellpadding=10>
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| 292 | <tr>
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| 293 | <td><tt>G4bool GetPDGStable()</tt>
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| 294 | <td>stable flag
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| 295 | <tr>
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| 296 | <td><tt>G4double GetPDGLifeTime()</tt>
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| 297 | <td>life time
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| 298 | <tr>
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| 299 | <td><tt>G4DecayTable* GetDecayTable()</tt>
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| 300 | <td>decay table
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| 301 | <tr>
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| 302 | <td align=center colspan=2>
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| 303 | Table 5.3.2<BR>
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| 304 | Methods to get particle decay modes and life time.
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| 305 | </td>
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| 306 | </tr>
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| 307 | </table></center>
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| 308 | <p>
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| 309 | Users can modify these properties, though the other properties listed above can not be change without rebuilding the libraries.
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| 310 | <P>
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| 311 | <i>G4ParticleDefinition</i> provides methods for setting and/or getting cut off values, as
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| 312 | shown in Table 5.3.3.
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| 313 | <p>
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| 314 | However, these methods only provide the functionality to set and get values.
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| 315 | Calculation of energy cut-off values from a cut-off value in range
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| 316 | is implemented in the <i>G4ParticleWithCuts</i> class, as described below.
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| 317 | <P>
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| 318 | In addition, each particle has its own <i>G4ProcessManger</i> object that manages a list of
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| 319 | processes applicable to the particle.
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| 320 | <P>
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| 321 |
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| 322 | <HR>
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| 323 | <a name="5.3.3">
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| 324 | <H2>5.3.3 Dynamic particle</H2></a>
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| 325 |
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| 326 | The <i>G4DynamicParticle</i> class has kinematics information for the particle
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| 327 | and is used for describing the dynamics of physics processes.
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| 328 | The properties in <i>G4DynamicParticle</i> are listed in Table 5.3.4.
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| 329 | <p>
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| 330 | <center><table border=2 cellpadding=10>
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| 331 | <tr>
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| 332 | <td><tt>G4double theDynamicalMass</tt>
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| 333 | <td>dynamical mass
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| 334 | <tr>
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| 335 | <td><tt>G4ThreeVector theMomentumDirection</tt>
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| 336 | <td>normalized momentum vector
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| 337 | <tr>
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| 338 | <td><tt>G4ParticleDefinition* theParticleDefinition</tt>
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| 339 | <td>definition of particle
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| 340 | <tr>
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| 341 | <td><tt>G4ThreeVector thePolarization</tt>
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| 342 | <td>polarization vector
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| 343 | <tr>
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| 344 | <td><tt>G4double theKineticEnergy</tt>
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| 345 | <td>kinetic energy
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| 346 | <tr>
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| 347 | <td><tt>G4double theProperTime</tt>
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| 348 | <td>proper time
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| 349 | <tr>
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| 350 | <td><tt>G4ElectronOccupancy* theElectronOccupancy</tt>
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| 351 | <td>electron orbits for ions
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| 352 | <tr>
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| 353 | <td align=center colspan=2>
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| 354 | Table 5.3.4<BR>
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| 355 | Methods to set/get cut off values.
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| 356 | </td>
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| 357 | </tr>
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| 358 | </table></center>
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| 359 | <p>
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| 360 | Here, the dynamical mass is defined as the mass for the dynamic particle.
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| 361 | For most cases, it is same as the mass defined in <i>G4ParticleDefinition</i> class
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| 362 | ( i.e. mass value given by <tt>GetPDGMass()</tt> method). However, there are
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| 363 | two exceptions.
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| 364 | <ul>
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| 365 | <li> resonace particle
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| 366 | <li> ions
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| 367 | </ul>
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| 368 | Resonace particles have large mass width and the total energy of decay products
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| 369 | at the center of mass system can be different event by event.
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| 370 | <p>
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| 371 | As for ions, <i>G4ParticleDefintion</i> defines a nucleus and <i>G4DynamicParticle</i>
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| 372 | defines an atom. <i>G4ElectronOccupancy</i> describes state of orbital electrons.
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| 373 | So, the dynaimc mass can be different from the PDG mass by the mass of electrons
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| 374 | (and their binding energy).
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| 375 | <p>
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| 376 | Decay products of heavy flavor particles are given in many event generators.
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| 377 | In such cases, <i>G4VPrimaryGenerator</i> sets this information
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| 378 | in <tt>*thePreAssignedDecayProducts</tt>. In addition, decay time of
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| 379 | the particle can be set arbitrarily time by using <tt>PreAssignedDecayProperTime</tt>.
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| 380 | <P>
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| 381 |
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| 382 | <BR><BR>
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| 383 | <HR>
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| 384 | <A HREF="../../../../Authors/html/subjectsToAuthors.html">
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| 385 | <I>About the authors</I></A>
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| 386 |
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| 387 | </BODY>
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| 388 | </HTML>
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