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26 #ifndef PAR03EMSHOWERMODEL_HH
27 #define PAR03EMSHOWERMODEL_HH
28
29 #include "G4VFastSimulationModel.hh"
30
31 class Par03EMShowerMessenger;
32 class G4FastSimHitMaker;
33
34 /**
35 * @brief Example fast simulation model for EM showers.
36 *
37 * Parametrisation of electrons, positrons, and gammas. It is triggered if those
38 * particles enter the detector so that there is sufficient length for the
39 * shower development (max depth, controlled by the UI command).
40 *
41 * Parametrisation is based on the PDG chapter on the electromagnetic cascades
42 * (chapter 33.5). Longitudinal profile of the shower is described with Gamma
43 * distribution, with beta parameter on average equal to 0.5 (default value,
44 * Fig. 33.21), and alpha parameter calcluated from the incident particle energy
45 * and material of the detector (critical energy) following Eq.(33.36).
46 *
47 * Transverse profile is in this model approximated by the Gaussian
48 * distribution, with the mean along the shower axis (incident particle momentum
49 * direction) and the standard deviation calculated from the detector material
50 * (Moliere radius). This assumes that EM shower is in 90% contained within a
51 * cylinder of radius equal to Moliere radius, and that area below Gaussian
52 * distribution from `mean-1.645 sigma` to `mean+1.645 sigma` is also equal to
53 * 90% of total distribution.
54 *
55 * Parameters of both distributions (alpha, beta for Gamma, sigma for Gaussian)
56 * can be overwritten by UI commands.
57 *
58 * Parametrisation creates N hits of same energy (N can be set by UI command),
59 * using rejection sampling to generate position along shower axis from Gamma
60 * distribution, and then sampling from uniform and Gaussian distributions to
61 * sample phi and radius, respectively. Created hits are deposited in the
62 * detector using its readout geometry, using the helper class G4FastSimHitMaker
63 * that locates the volume, and calls appropriate sensitive detector class.
64 *
65 * PDG Chapter 33:
66 * https://pdg.lbl.gov/2019/reviews/rpp2018-rev-passage-particles-matter.pdf
67 *
68 */
69
70 class Par03EMShowerModel : public G4VFastSimulationModel
71 {
72 public:
73 Par03EMShowerModel(G4String, G4Region*);
74 Par03EMShowerModel(G4String);
75 ~Par03EMShowerModel();
76
77 /// There are no kinematics constraints. True is returned.
78 virtual G4bool ModelTrigger(const G4FastTrack&) final;
79 /// Model is applicable to electrons, positrons, and photons.
80 virtual G4bool IsApplicable(const G4ParticleDefinition&) final;
81 /// Take particle out of the full simulation (kill it at the entrance
82 /// depositing all the energy). Calculate energy deposited in the detector
83 /// according to Gamma distribution (along the particle direction) and
84 /// Gaussian distribution in the transverse direction. Mean of the Gaussian is
85 /// centred on the shower axis. Create energy deposits on a cylindrical mesh.
86 /// Parameters of the mesh (size, number of cells) and of the distributions
87 /// (alpha, beta for Gamma, sigma for Gaussian) can be set with UI commands.
88 virtual void DoIt(const G4FastTrack&, G4FastStep&) final;
89
90 /// Print current settings.
91 void Print() const;
92 /// Set standard deviation of a Gaussian distribution that describes the
93 /// transverse shower profile.
94 inline void SetSigma(const G4double aSigma) { fSigma = aSigma; };
95 /// Get standard deviation of a Gaussian distribution that describes the
96 /// transverse shower profile.
97 inline G4double GetSigma() const { return fSigma; };
98 /// Set alpha parameter of a Gamma distribution that describes the
99 /// longitudinal shower profile.
100 inline void SetAlpha(const G4double aAlpha) { fAlpha = aAlpha; };
101 /// Get alpha parameter of a Gamma distribution that describes the
102 /// longitudinal shower profile.
103 inline G4double GetAlpha() const { return fAlpha; };
104 /// Set beta parameter of a Gamma distribution that describes the longitudinal
105 /// shower profile.
106 inline void SetBeta(const G4double aBeta) { fBeta = aBeta; };
107 /// Get beta parameter of a Gamma distribution that describes the longitudinal
108 /// shower profile.
109 inline G4double GetBeta() const { return fBeta; };
110 /// Set number of (same energy) hits created in the parametrisation.
111 inline void SetNbOfHits(const G4int aNumber) { fNbOfHits = aNumber; };
112 /// Get number of (same energy) hits created in the parametrisation.s
113 inline G4int GetNbOfHits() const { return fNbOfHits; };
114 /// Set maximum depth of shower created in fast simulation. It is expressed in
115 /// units of radiaton length.
116 inline void SetLongMaxDepth(const G4double aDepth) { fLongMaxDepth = aDepth; };
117 /// Get maximum depth of shower created in fast simulation. It is expressed in
118 /// units of radiaton length.
119 inline G4double GetLongMaxDepth() const { return fLongMaxDepth; };
120
121 private:
122 /// Gamma distribution
123 inline G4double Gamma(G4double x, G4double alpha, G4double beta)
124 {
125 return (std::pow(beta, alpha) / std::tgamma(alpha) * std::pow(x, alpha - 1)
126 * std::exp(-beta * x));
127 }
128 /// Gaussian distribution
129 inline G4double Gaussian(G4double x, G4double sigma = 1, G4double x0 = 0)
130 {
131 G4double tmp = (x - x0) / sigma;
132 return (1.0 / (std::sqrt(2 * CLHEP::pi) * sigma)) * std::exp(-tmp * tmp / 2);
133 }
134
135 private:
136 /// Messenger for configuration
137 Par03EMShowerMessenger* fMessenger;
138 /// Helper class for creation of hits within the sensitive detector
139 std::unique_ptr<G4FastSimHitMaker> fHitMaker;
140 /// Standard deviation of the Gaussian distribution
141 /// Can be changed with UI command `/Par03/fastSim/transverseProfile/sigma
142 /// <sigma>`
143 /// If sigma is smaller than 0, it will be estimated from the detector
144 /// material (Moliere radius).
145 G4double fSigma = -1;
146 /// Alpha parameter of the Gamma distribution
147 /// Can be changed with UI command `/Par03/fastSim/longitudunalProfile/alpha
148 /// <alpha>`
149 /// If alpha is smaller than 0, it will be estimated from particle energy and
150 /// the detector material.
151 G4double fAlpha = -1;
152 /// Beta parameter of the Gamma distribution
153 /// Can be changed with UI command `/Par03/fastSim/longitudinalProfile/beta
154 /// <beta>`
155 G4double fBeta = 0.5;
156 /// Number of (same energy) hits created by the parametrisation. Can be
157 /// changed with UI command `/Par03/fastSim/numberOfHits <number>`
158 G4int fNbOfHits = 100;
159 /// Maximum depth of a shower created in fast simulation.
160 /// It is expressed in units of radiation length. Can be changed with UI
161 /// command `/Par03/fastSim/longitudinalProfile/maxDepth <depth>`
162 G4double fLongMaxDepth = 30;
163 };
164 #endif /* PAR03EMSHOWERMODEL_HH */