Par03/include/Par03EMShowerModel.hh

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0026 /// \file Par03EMShowerModel.hh
0027 /// \brief Definition of the Par03EMShowerModel class
0028
0029 #ifndef PAR03EMSHOWERMODEL_HH
0030 #define PAR03EMSHOWERMODEL_HH
0031
0032 #include "G4VFastSimulationModel.hh"
0033
0034 class Par03EMShowerMessenger;
0035 class G4FastSimHitMaker;
0036
0037 /**
0038  * @brief Example fast simulation model for EM showers.
0039  *
0040  * Parametrisation of electrons, positrons, and gammas. It is triggered if those
0041  * particles enter the detector so that there is sufficient length for the
0042  * shower development (max depth, controlled by the UI command).
0043  *
0044  * Parametrisation is based on the PDG chapter on the electromagnetic cascades
0045  * (chapter 33.5). Longitudinal profile of the shower is described with Gamma
0046  * distribution, with beta parameter on average equal to 0.5 (default value,
0047  * Fig. 33.21), and alpha parameter calcluated from the incident particle energy
0048  * and material of the detector (critical energy) following Eq.(33.36).
0049  *
0050  * Transverse profile is in this model approximated by the Gaussian
0051  * distribution, with the mean along the shower axis (incident particle momentum
0052  * direction) and the standard deviation calculated from the detector material
0053  * (Moliere radius). This assumes that EM shower is in 90% contained within a
0054  * cylinder of radius equal to Moliere radius, and that area below Gaussian
0055  * distribution from `mean-1.645 sigma` to `mean+1.645 sigma` is also equal to
0056  * 90% of total distribution.
0057  *
0058  * Parameters of both distributions (alpha, beta for Gamma, sigma for Gaussian)
0059  * can be overwritten by UI commands.
0060  *
0061  * Parametrisation creates N hits of same energy (N can be set by UI command),
0062  * using rejection sampling to generate position along shower axis from Gamma
0063  * distribution, and then sampling from uniform and Gaussian distributions to
0064  * sample phi and radius, respectively. Created hits are deposited in the
0065  * detector using its readout geometry, using the helper class G4FastSimHitMaker
0066  * that locates the volume, and calls appropriate sensitive detector class.
0067  *
0068  * PDG Chapter 33:
0069  * https://pdg.lbl.gov/2019/reviews/rpp2018-rev-passage-particles-matter.pdf
0070  *
0071  */
0072
0073 class Par03EMShowerModel : public G4VFastSimulationModel
0074 {
0075   public:
0076     Par03EMShowerModel(G4String, G4Region*);
0077     Par03EMShowerModel(G4String);
0078     ~Par03EMShowerModel();
0079
0080     /// There are no kinematics constraints. True is returned.
0081     virtual G4bool ModelTrigger(const G4FastTrack&) final;
0082     /// Model is applicable to electrons, positrons, and photons.
0083     virtual G4bool IsApplicable(const G4ParticleDefinition&) final;
0084     /// Take particle out of the full simulation (kill it at the entrance
0085     /// depositing all the energy). Calculate energy deposited in the detector
0086     /// according to Gamma distribution (along the particle direction) and
0087     /// Gaussian distribution in the transverse direction. Mean of the Gaussian is
0088     /// centred on the shower axis. Create energy deposits on a cylindrical mesh.
0089     /// Parameters of the mesh (size, number of cells) and of the distributions
0090     /// (alpha, beta for Gamma, sigma for Gaussian) can be set with UI commands.
0091     virtual void DoIt(const G4FastTrack&, G4FastStep&) final;
0092
0093     /// Print current settings.
0094     void Print() const;
0095     /// Set standard deviation of a Gaussian distribution that describes the
0096     /// transverse shower profile.
0097     inline void SetSigma(const G4double aSigma) { fSigma = aSigma; };
0098     /// Get standard deviation of a Gaussian distribution that describes the
0099     /// transverse shower profile.
0100     inline G4double GetSigma() const { return fSigma; };
0101     /// Set alpha parameter of a Gamma distribution that describes the
0102     /// longitudinal shower profile.
0103     inline void SetAlpha(const G4double aAlpha) { fAlpha = aAlpha; };
0104     /// Get alpha parameter of a Gamma distribution that describes the
0105     /// longitudinal shower profile.
0106     inline G4double GetAlpha() const { return fAlpha; };
0107     /// Set beta parameter of a Gamma distribution that describes the longitudinal
0108     /// shower profile.
0109     inline void SetBeta(const G4double aBeta) { fBeta = aBeta; };
0110     /// Get beta parameter of a Gamma distribution that describes the longitudinal
0111     /// shower profile.
0112     inline G4double GetBeta() const { return fBeta; };
0113     /// Set number of (same energy) hits created in the parametrisation.
0114     inline void SetNbOfHits(const G4int aNumber) { fNbOfHits = aNumber; };
0115     /// Get number of (same energy) hits created in the parametrisation.s
0116     inline G4int GetNbOfHits() const { return fNbOfHits; };
0117     /// Set maximum depth of shower created in fast simulation. It is expressed in
0118     /// units of radiaton length.
0119     inline void SetLongMaxDepth(const G4double aDepth) { fLongMaxDepth = aDepth; };
0120     /// Get maximum depth of shower created in fast simulation. It is expressed in
0121     /// units of radiaton length.
0122     inline G4double GetLongMaxDepth() const { return fLongMaxDepth; };
0123
0124   private:
0125     /// Gamma distribution
0126     inline G4double Gamma(G4double x, G4double alpha, G4double beta)
0127     {
0128       return (std::pow(beta, alpha) / std::tgamma(alpha) * std::pow(x, alpha - 1)
0129               * std::exp(-beta * x));
0130     }
0131     /// Gaussian distribution
0132     inline G4double Gaussian(G4double x, G4double sigma = 1, G4double x0 = 0)
0133     {
0134       G4double tmp = (x - x0) / sigma;
0135       return (1.0 / (std::sqrt(2 * CLHEP::pi) * sigma)) * std::exp(-tmp * tmp / 2);
0136     }
0137
0138   private:
0139     /// Messenger for configuration
0140     Par03EMShowerMessenger* fMessenger;
0141     /// Helper class for creation of hits within the sensitive detector
0142     std::unique_ptr<G4FastSimHitMaker> fHitMaker;
0143     /// Standard deviation of the Gaussian distribution
0144     /// Can be changed with UI command `/Par03/fastSim/transverseProfile/sigma
0145     /// <sigma>`
0146     /// If sigma is smaller than 0, it will be estimated from the detector
0147     /// material (Moliere radius).
0148     G4double fSigma = -1;
0149     /// Alpha parameter of the Gamma distribution
0150     /// Can be changed with UI command `/Par03/fastSim/longitudunalProfile/alpha
0151     /// <alpha>`
0152     /// If alpha is smaller than 0, it will be estimated from particle energy and
0153     /// the detector material.
0154     G4double fAlpha = -1;
0155     /// Beta parameter of the Gamma distribution
0156     /// Can be changed with UI command `/Par03/fastSim/longitudinalProfile/beta
0157     /// <beta>`
0158     G4double fBeta = 0.5;
0159     /// Number of (same energy) hits created by the parametrisation. Can be
0160     /// changed with UI command `/Par03/fastSim/numberOfHits <number>`
0161     G4int fNbOfHits = 100;
0162     /// Maximum depth of a shower created in fast simulation.
0163     /// It is expressed in units of radiation length. Can be changed with UI
0164     /// command `/Par03/fastSim/longitudinalProfile/maxDepth <depth>`
0165     G4double fLongMaxDepth = 30;
0166 };
0167 #endif /* PAR03EMSHOWERMODEL_HH */