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0002
0003 =========================================================
0004 Geant4 - an Object-Oriented Toolkit for Simulation in HEP
0005 =========================================================
0006
0007 TestEm15
0008 --------
0009
0010 How to compute and plot the final state of:
0011 - Multiple Scattering
0012 - Gamma Conversion
0013 considered as an isolated processes, see PHYSICS.
0014
0015 For Multiple Scattering, the method is exposed below.
0016
0017 For Gamma Conversion, when G4BetheHeitler5DModel Model is used.
0018
0019 1- GEOMETRY DEFINITION
0020
0021 It is a single box representing a 'semi infinite' homogeneous medium.
0022 Two parameters define the geometry:
0023 - the material of the box,
0024 - the (full) size of the box.
0025
0026 The default geometry (100 m of water) is constructed in
0027 DetectorConstruction, but the above parameters can be changed
0028 interactively via the commands defined in DetectorMessenger.
0029
0030 2- PHYSICS LIST
0031
0032 The physics list contains the standard electromagnetic processes.
0033 In order not to introduce 'artificial' constraints on the step size,
0034 there is no limitation from the maximum energy lost per step.
0035
0036 3- AN EVENT: THE PRIMARY GENERATOR
0037
0038 The primary kinematic consists of a single particle starting at the edge
0039 of the box. The type of the particle and its energy are set in
0040 PrimaryGeneratorAction (1 MeV electron), and can be changed via the G4
0041 build-in commands of ParticleGun class (see the macros provided with
0042 this example).
0043
0044 4- PHYSICS
0045
0046 All discrete processes are inactivated (see provided macros),
0047 so that Multiple Scattering or Gamma Conversion is 'forced' to
0048 determine the first step of the primary particle.
0049 The step size and the final state are computed and plotted.
0050 Then the event is immediately killed.
0051
0052 Multiple Scattering:
0053
0054 The result is compared with the 'input' data, i.e. with the cross
0055 sections stored in the PhysicsTables and used by Geant4.
0056 The stepMax command provides an additional control of the step size of
0057 the multiple scattering.
0058
0059
0060 5- HISTOGRAMS
0061
0062 The test contains 16 built-in 1D histograms, which are managed by
0063 G4AnalysisManager and its Messenger. The histos can be individually
0064 activated with the command:
0065 /analysis/h1/set id nbBins valMin valMax unit
0066 where unit is the desired unit for the histo (MeV or keV, etc..)
0067 (see the macros xxxx.mac).
0068
0069 1 Multiple Scattering. True step length
0070 2 Multiple Scattering. Geom step length
0071 3 Multiple Scattering. Ratio geomSl/trueSl
0072 4 Multiple Scattering. Lateral displacement: radius
0073 5 Multiple Scattering. Lateral displac: psi_space
0074 6 Multiple Scattering. Angular distrib: theta_plane
0075 7 Multiple Scattering. Phi-position angle
0076 8 Multiple Scattering. Phi-direction angle
0077 9 Multiple Scattering. Correlation: cos(phiPos-phiDir)
0078
0079 10 Gamma Conversion. Open Angle * Egamma
0080 11 Gamma Conversion. Log10(P recoil)
0081 12 Gamma Conversion. Phi P recoil angle
0082 13 Gamma Conversion. Phi P plus angle
0083 14 Gamma Conversion. 2 * cos(phiplus + phiminus) Asymmetry
0084 15 Gamma Conversion. E plus / E gamma
0085 16 Gamma Conversion. Phi of Gamma Polarization
0086
0087
0088 The histograms are managed by the HistoManager class and its Messenger.
0089 The histos can be individually activated with the command:
0090 /analysis/h1/set id nbBins valMin valMax unit
0091 where unit is the desired unit for the histo (MeV or keV, deg or mrad, etc..)
0092
0093 One can control the name of the histograms file with the command:
0094 /analysis/setFileName name (default testem15)
0095
0096 It is possible to choose the format of the histogram file : root (default),
0097 hdf5, xml, csv, by changing the default file type in HistoManager.cc
0098
0099 It is also possible to print selected histograms on an ascii file:
0100 /analysis/h1/setAscii id
0101 All selected histos will be written on a file name.ascii (default testem15)
0102
0103 6- VISUALIZATION
0104
0105 The Visualization Manager is set in the main().
0106 The initialization of the drawing is done via the commands
0107 /vis/... in the macro vis.mac. To get visualization:
0108 > /control/execute vis.mac
0109
0110 The detector has a default view which is a longitudinal view of the
0111 box.
0112
0113 The tracks are drawn at the end of event, and erased at the end of run.
0114
0115 7- HOW TO START ?
0116
0117 execute TestEm15 in 'batch' mode from macro files:
0118 % TestEm15 compt.mac
0119
0120 execute TestEm15 in 'interactive mode' with visualization:
0121 % TestEm15
0122 Idle> control/execute vis.mac
0123 ....
0124 Idle> type your commands
0125 ....
0126 Idle> exit
0127
0128 8 - MACROS
0129 The examples of macros for Multiple Scattering:
0130 electron.mac muon.mac proton.mac
0131
0132 The example of Gamma Conversion macro:
0133 gamma.mac - gamma to e+ e-
0134
0135 9 - HISTOGRAMS for gamma conversion
0136
0137 10 # Open Angle (rad)* E gamma (MeV)
0138 The most probable value of the e+ e- pair opening angle multiplied by the
0139 photon energy is 1.6 rad*MeV and 338 rad*MeV in case mu+ mu- pair.
0140 See: Olsen, Phys. Rev. 131 (1963) 406.
0141 See also: Fig. 7 of arXiv:1802.08253 and Fig. 6 arXiv:1910.12501.
0142
0143 11 # Log10 ( recoil momentum)
0144 The distribution of the recoil momentum is described by
0145 Jost, Phys. Rev. 80 (1950) 189 (no form factor).
0146 See also Fig. 2 of Astroparticle Physics 88 (2017) 60.
0147
0148 12 # Phi recoil
0149 13 # Phi positron
0150 For linearly polarized incident photons, the distributions should show
0151 a sinusoidal shape with period 180°, for non polarized incident photons,
0152 the distribution of azimuthal angles should be flat.
0153
0154
0155 14 # Asymmetry 2 * cos(phi_+ + phi_-)
0156 For a photon propagating along x, polarized along y,
0157 the average value of ( 2.0 * cos(phi_+ + phi_-) ),
0158 provides a measurement of the polarization asymmetry, A.
0159 Eq. (12) of Nucl. Instrum. Meth. A 729 (2013) 765
0160 The azimuthal angle of the event defined as the bisector angle
0161 of the azimuthal angles of the positron and of the electron,
0162 (phi_+ + phi_-)/2,
0163 provides the optimal measurement of the asymmetry
0164 Astroparticle Physics 88 (2017) 30.
0165
0166 For high-energy photons (E >> 20 MeV), the asymptotic expression for A
0167 can be used for comparison.
0168 Boldyshev, Yad. Fiz. 14 (1971) 1027, Sov.J.Nucl.Phys. 14 (1972) 576.
0169 See also eq. (13) of arXiv:1802.08253
0170 Example : A ~ 0.17 at 100 GeV.
0171
0172 15 # E plus / E gamma
0173 x_+ = E plus / E gamma has a more-or-less flat spectrum that extends
0174 almost from 0. to 1.
0175 See Fig. 16 page 261 of "The Quantum Theory of Radiation", W. Heitler,
0176 3rd edition, 1954.
0177
0178 16 # Phi of Gamma Polarization
0179 The phi of polarization vector after transformation into reference system
0180 defined by gamma direction (z) , gamma polarization (x).
0181
0182 10 - UI COMMANDS
0183
0184 There are two commands to control G4BetheHeitler5DModel:
0185
0186 /process/gconv/conversionType itype
0187 /process/gconv/onIsolated bool
0188
0189 The command:
0190 /process/gconv/conversionType
0191
0192 Allow to force conversion on nuclear or electron
0193 The parameter values
0194 0 - (default) both triplet and nuclear conversion in proportion triplet/nuclear 1/Z
0195 1 - force nuclear conversion
0196 2 - force triplet
0197
0198 The command:
0199 /process/gconv/onIsolated
0200
0201 Allow simulate conversion on isolated particles without screening
0202 The perimeter values:
0203 false - (default) atomic electron screening
0204 true - conversion on isolated particles
